# Posts by David

Total # Posts: 2,287

**chemistry**

An Erlenmeyer flask containing a hot solution is not tightly stoppered to prevent solvent loss during cooling. give reasons.

**chemistry**

A hot recrystallization solution is not filtered unless absolutely necessary.give reason.

**Physics**

A ball is thrown from a point 1.38 m above the ground. The initial velocity is 19.9 m/s at an angle of 33.8° above the horizontal. Find the maximum height of the ball above the ground. Calculate the speed of the ball at the highest point in the trajectory.

**Chemistry**

A chemist conducted a recrystallization on 18.5 g of a solid and collected 12.5 g from the first, and 2.7 g from the second recrystallization. Show your calculation and answer the following questions: What is the percent recovery in the first recrystallization? (1.5 marks) ...

**Chemistry**

• A student crystallized a compound from benzene and observed only a few crystals when the solution cooled to room temperature. To increase the yield of crystals, the students chilled the mixture in an ice-water bath. The chilling greatly increased the quantity of solid ...

**Chemistry**

Carborundum (silicon carbide) boiling chips are better than calcium carbonate chips in the recrystallization of an unknown,why ?

**Chemistry**

Carborundum (silicon carbide) boiling chips are better than calcium carbonate chips in the recrystallization of an unknown,why ?

**Chemistry**

The solubility of acetanilide in hot water (5.5 g/100 mL at 100C) is not very great, and its solubility in cold water (0.53 g/100 mL at 0C) is significant. What would be the maximum theoretical percent recovery from the first recrystallization of 0.5 g of acetanilide from 100 ...

**Chemistry**

Why can a water-ethanol solution be used for recrystallization but not a water-hexane solution?

**Chemistry**

The solubility of compound A in ethanol is 0.4 g per 100 mL at 0C and 5.0 g per 100 mL at 78C. What is the minimum amount of solvent needed to recrystallize an 8.0 g sample of compound A? How much would be lost in the recrystallization? Show your work.

**Chemistry**

After treating a coloured solution of a compound with activated charcoal, filtering and drying the product, the colour of the product was grey. What caused the grey colour? How can the grey colour be removed?

**chemistry**

explain the term carbonate error ..

**Physics**

A person walks the path shown below. The total trip consists of four straight-line paths. Path 1 is 40.0 m due east. Path 2 is 170.0 m due south. Path 3 is 120.0 m 30.0° south of west. Path 4 is 190.0 m 60.0° north of west. At the end of the walk, what is the person&#...

**math**

It is estimated that one third of one per cent of the Earth’s surface receives more energy from the sun than the total projected needs for the year 2014. Assuming the Earth’s surface to be 1.97 x 108 square miles. Find the area in acres.

**Math**

a/(a+2)-1 = -(3a+2)/(a^2+4a+4)

**math**

It is estimated that one third of one per cent of the Earth’s surface receives more energy from the sun than the total projected needs for the year 2014. Assuming the Earth’s surface to be 1.97 x 108 square miles. Find the area in acres.

**math**

How many liters of gasoline are there in 165 gal (US) of a methanol-gasoline blend that is 11.0% by volume?

**math**

A chemical distillation tower, 110 m high is supported by cables of length L that reach from the top of the column to the ground at a distance D from the base of the tower. If D is 1/3 the length of a cable, find L and D.

**7th Grade Science**

Identify 5 characteristics common to plants and describe them?

**math**

Write a number which rounds to 66,000 when rounded to the nearest ten thousand

**psychology**

when kevin started his car in the parking lot, he also turned on the radio to his favorite station,as he entered the street onto the campus, he turned the radio up due to the increased background noise in the car. entering the highway, he again increased the volume until he ...

**math**

Alex spent 3/7 of his money. He gave 1/4 of the remainder to his sister. He had $120 left. How much money did he have in the beginning?

**physics**

A roller coaster travels 196ft at an angle of 61.1° above horizantally. How far does it travel horizantally?

**Math**

an air traffic controller spots two planes at the same altitude flying towards one another. their flight paths form a right angle at point p. One plane is 150 miles from point p and is moving 450mph. the other plane is moving at 450mph but is 200 miles from point p. write the ...

**Precalculus**

an air traffic controller spots two planes at the same altitude flying towards one another. their flight paths form a right angle at point p. One plane is 150 miles from point p and is moving 450mph. the other plane is moving at 450mph but is 200 miles from point p. write the ...

**Math**

what does -1 E-4 mean when you write it out?

**Physics**

You are traveling on an airplane. The velocity of the plane with respect to the air is 110.0 m/s due east. The velocity of the air with respect to the ground is 39.0 m/s at an angle of 30° west of due north. 1) What is the speed of the plane with respect to the ground? 2) ...

**algebra**

(3,0),0,-4).solve for length, standard form.thank you

**algebra**

(3,0),0,-4).solve for length, standard form.

**algebra**

(3,0),0,-4).solve for the following :

**Health**

The answer is K ;)

**Math**

Find the half-life (in hours) of a radioactive substance that is reduced by 10 percent in 5 hours.

**physics**

A red ball is thrown down with an initial speed of 1.0 m/s from a height of 27.0 meters above the ground. Then, 0.6 seconds after the red ball is thrown, a blue ball is thrown upward with an initial speed of 24.5 m/s, from a height of 0.7 meters above the ground. The force of ...

**Physics**

A tortoise and hare start from rest and have a race. As the race begins, both accelerate forward. The hare accelerates uniformly at a rate of 0.8 m/s2 for 4.4 seconds. It then continues at a constant speed for 13.5 seconds, before getting tired and slowing down with constant ...

**physics with 6 questions**

Two cars start from rest at a red stop light. When the light turns green, both cars accelerate forward. The blue car accelerates uniformly at a rate of 3.3 m/s2 for 3.9 seconds. It then continues at a constant speed for 13.7 seconds, before applying the brakes such that the ...

**Physic**

Type A nerve fibers in humans can conduct nerve impulses at speeds up to 139.8 m/s. How fast is this in mph? This is a question from my physic homework. I have tried converting 139.8 m/s to mile then to hrs and i got .000241 mph. When I input it it said this is not correct. ...

**physics**

A rolling ball moves from x1 = 3.2 cm to x2 = -4.2 cm during the time from t1 = 3.8 s to t2 = 6.1 s. What is its average velocity?

**math**

Estimate. 247 * 974 a. Write your estimate as a number sentence: ________________ b. How I estimated : ________________________________

**Stats**

Question 3 Investment analysts generally believe the interest rate on bonds is inversely related to the prime interest rate for loans; that is, bonds perform well when lending rates are down and perform poorly when interest rates are up. Can the bond rate be predicted by the ...

**Stats**

This assignment requires you to use Excel. In question 1, you will use the charting features. In questions 2 and 3, use the regression tool from the analysis toolpack. There is no template for this assignment. Make sure you explain your answers and provide the regression ...

**Math**

Joelle earns her regular pay of 7.50 per hour for up to 40 hours a week. for each hour over 40 hours of work in a week, joelle is paid 1.5 times her regular pay. how much does joelle earn for a week in which she works 42 hours?

**psychology**

After watching golf on TV several times with her father, 7-year-old Michelle learned how to swing a club even before she actually had one in her hands. What kind of learning took place?

**health**

HAHAHA ME TOO THIS ANSWERS ARE REALLY HELPFUL THANKS

**Physics**

How long would it take a car engine, say 500 pounds of iron, to cool from 1,200 degrees F (exauhst manifold temp) to air ambient temp. of 75 degrees F.

**Physic**

What is the source of the sun's energy?

**Stastistic**

Finde the mean , variance , standard deviation N-127, P=0.66

**math**

Frank's cell phone package costs $20 per month and an additional $0.05 per text. Josie pays $15 per month and $0.10 per minute. Determine the linear system that could be used to find out when their monthly bills would be the same.

**MATH**

Find the amount of interest and the monthly payment for the loan. Purchase a living room set for $3,800 at 12% add-on interest for 3 years.

**statistics**

Surgery vs. placebo for the knee pain: Refer to Example 10. Is Arthroscopic Surgery Better than Placebo? Here we show MINITAB output comparing mean knee pain scores for the placebo (group 1) to debridement arthroscopic surgery (group 2). a) State and interpret the result of ...

**Physic**

What are some sources of energy that are available to heat the interiors of planets?

**science**

2 WAYS TO DETERMINE THE INTERIOR ARE GRAVITY, AND SEISMOLOGY.

**Science**

How can we use Kepler's laws or Newton's laws to learn about these objects?

**Astronomy**

How were the different objects in the solar system discovered? What are the properties of the ice giants?

**Physic**

alive

**calculus**

How do I take the partial derivative of P with respect to r of the following: D ~ P = ‡”(t=1 to T)[t ~ (CF)_t/(1+r)^t ]

**math**

5x-y=22 x+9y=32

**Physics?**

In Rutherford's scattering experiments, alpha particles (charge = +2e) were fired at a gold foil. Consider an alpha particle, very far from the gold foil, with an initial kinetic energy of 2.0 MeV heading directly for a gold atom (charge +79e). The alpha particle will ...

**math**

5040

**Alg/Trig**

(x-2)^2 + (y-3)^2 = 4.5^2

**math ( pre algebra )**

B. H

**math**

nonsense. let the three batteries by A,B,C then A = 2B 3A = C A + B + C = 54 so A = 12 B = 6 C = 36

**math**

How do I take the partial derivative of P with respect to r of the following: D × P = ∑(t=1 to T)[t × (CF)_t/(1+r)^t ]

**Algebra 2**

Thanks Ms Sue its my daughters problem ,my responce was maybe the wording might be asking "what investment " might be what amounts in what types of investments would yield the $4ooo. Or it might be just be about the math and analizing it. Either way ,thank you

**Algebra 2**

As a graduation present, you want to gift your son a trip to Disney World. Presently beginning his second semester as a high school junior, you hope you have enough time to save $4,000 to support much of the trips expenses for your child and two of his closest friends. Rather ...

**english/grammar**

I need help editing errors in parallelism in the following sentence: Is it true that Superman could leap tall buildings, run faster than a locomotive, and that bullets would bounce off his skin?

**105 personal dimension of education**

my classes start 5-29-`12, can I get a better idea of whats ahead of me(course description)or what it consist of. Thank you

**grammar**

ops whats the first one

**grammar**

Whats the last one?

**physics**

or I've kept up with my homework and work this whole year except that our teacher just randomly decided to give us a ton of homework this weekend, and I have done all I can do. All of my friends are in the physics 1 class while this is physics 2 so no I cannot have answers...

**physics**

Hi, my teacher doesn't teach us too well and we have a few packets to hand in for tomorrow that I really don't understand much of. If someone could give me the answers to all of the problems on the first link if you search "the electrical energy converted to ...

**Geometry word problem**

A rectangular pond is 10m longer than it is wide. A walk 2m wide surrounds the pond. Find the dimensions of the pond if the area of the walk is 216m2

**Geometry**

A rectangualar playground is 4 meters longer than it is wide. If the length is increased by 5m, and the width decreased b y 1 m, the area is increased by 15m SQUARED(15M2).Find the original dimensions of the playground.

**Math**

How do i solve 2x+y > -3? And how do i graph it. This is Linear inequalities.

**phisycal sciences**

Which of the following properties did Rutherford use in his experiment? A. the negative charge of the alpha particles and the random distribution of protons B. the negative charge of the alpha particles and the positive charge of the gold foil C. the positive charge of the ...

**Mathematics**

Two numbers have thousandths other than zero. Could the difference of these numbers be 5.3? Explain.

**algebra 2**

Write an equation for a parabola with vertex at (3,- 6) and focus at (3,- 4).

**chemistry**

Is beta particles the answer?

**chemistry**

Which radioactive emanations have a charge of -1? beta particles alpha particles gamma rays neutrons

**Algebra**

-4x+1-2(x-1)= -4(x-4)

**algebra**

Write an equation of the hyperbola with foci (0, ) and (0, 2) and vertices of (0, ) and (0, 1).

**spanish**

Escribe el cual (la cual, los cuales, las cuales) o lo cual en el espacio. Nos invitaron a cenar con ellos, ____ fue una buena idea.

**spanish**

¿Cuál frase es correcta? El hijo del maestro, quien estuvo en mi clase, es muy inteligente. El hijo del maestro, a quien estuvo en mi clase, es muy inteligente.

**algebra**

When you spend $1 at the grocery store, the store doesn’t keep all of your money as profit. Some of it is reinvested in the economy when the grocery store buys more merchandise from suppliers. In turn, the suppliers don’t keep all of that money as profit, either; ...

**Finance**

Calculate the weighted cost of equity for a firm with the following characteristics: (a) Last Dividend--$5.00, (b) Growth Rate—6%, (c) Price of Stock--$125.00 and (d) Weight of Equity Capital—40%

**English**

Help me to write these answer question, Write an essay that illustrate the saying every cloud has a silver lining in 340 words

**American Lit.**

What is Fundamentalist-Modernist Controversy.? Is this one whole topic or more than one.?

**computer programming**

Make an Maplet that does the simple calculator funtions as addition, subtraction, multiplication, division, factorial, sin(), cos(), tan(). (using maplet in maplesoft)

**physics**

a one meter chain that weights one newton sits on a flat horizontal table that is one meter from the floor. the coefficient of friction between the chain and the table is 0.15. how much of the chain can dangle off the table until the chain pulls itself onto the floor? if it ...

**College Algebra**

log5 (x+2)+log5(x-2)=3

**algebra**

2(2x+5)-7<12 2(2(-5)+5)-7<12 2(-10+5)-7<12 2(-5)-7<12 -10-7<12 -17<12

**geometry**

A circle of radius r is centered at the origin and a rectangle is inscribed. The area of the rectangle as a function is given by what? Can you also explain the processes behind finding the answer it helps me understand.

**Environmental Science**

7 is D 10 is probably B because mosses are the first thing to grow naturally after the destruction of an environment like building a building 21 is D the y all effect marine ecosystems and are caused by humans 27 is D

**Chemistry**

Calculate the Concentration of Ni2+ in a soltion which prepared as mixing 50.0ml 0.0300 M Ni2+ and 50.0mlml 0.0500 M EDTA at pH= 3 At pH=3 , α4= 2.5x10-11 KNiY=4.2x1018

**Chemistry**

calculate the the pH of a buffer solution containing 0.246 M NH3 and 0.0954 M NH4Cl (for NH3 Kb = 1.74x 10-5)

**Chemistry**

what mass of AgBr is formed when a solution containing 3.45 g of KBr is mixed with a solution containing 7.28 g AgNO3?

**chemistry**

You have a 1 L container of a gas O 2 at 20°C and 1 atm. Subtracting the weight of the container, what is the mass of the gas?

**physics**

A truck covers m in 8 s while smoothly slowing down to a final speed of 2.8 m/s. (a) Find its initial speed. (b) Find its acceleration.

**Chemistry**

How many grams of water are formed when 250 mL of 2.0 M Mg(OH)2 are neutralized by a solution of HCL ?

**Chemistry**

How many mL of 3.0 M HCL are required to neutralize 250 mL of 2.0 M MgCL2 ?

**MaTh AlgeBRA**

Do synthetic division or long division Domain is all reals except x=1 because it gives you a 0 denominator.