Science

CHECK MY ANSWERS!!!!!!!
1) Cobalt has a mass number of 59 and an atomic number of 27. A student wants to create a model of a cobalt atom. Which statement about the model is correct?(1 point)

A. The model should show 27 protons and 32 neutrons.******
B. The model should show 59 protons and 27 neutrons.
C. The model should show 27 protons and 27 neutrons.
D. The model should show 32 protons and 59 neutrons.

2) In a molecule of lithium sulfide, there are two atoms of lithium and one atom of sulfur. Which statement about lithium sulfide is correct?(1 point)

A) The chemical formula for lithium sulfide is LiS2.
B) The atoms in lithium sulfide are held together by bonds.*****
C) Both lithium and sulfur form positive ions.
D) A molecular model of lithium sulfide would have two spheres.

3)Which element has the same number of valence electrons as bromine (Br)? (1 point)
A) ytterbium (Yb)
B) selenium (Se)
C) krypton (Kr)******
D) astatine (At)

4) Why are sodium (Na) and potassium (K) in the same group on the periodic table?(1 point)
A) They have similar reactivity.*******
B) They are both hard and brittle.
C) They have similar atomic weights.
D) They are both colorless.

5) A student cuts some fabric into two pieces. Is this change physical or chemical?(1 point)
A) It is a chemical change because there is no phase change.
B) It is a chemical change because the size changes.
C) It is a physical change because the process is reversible.
D) It is a physical change because there is no reaction.******

6) How are chemical changes different from physical changes?(1 point)
A) They form new substances.********
B) They are reversible.
C) They involve heat.
D) They include shifts in the phase of matter.

7)A scientist makes several observations about a chemical reaction and records them in the table shown. Which observation contains an error? (1 point) picture added!
A) 1
B) 3
C) 2******
D) 4

8) In a chemical reaction, hydrofluoric acid (HF) and sodium hydroxide (NaOH) combine to form sodium fluoride (NaF) and water (H2O). The reaction uses 20 grams of hydrofluoric acid and 40 grams of sodium hydroxide, and it produces 18 grams of water. How much sodium fluoride does the reaction produce?(1 point)

A) 60 grams
B) 42 grams
C) 18 grams******
D) 78 grams

9)Which procedure could be used to demonstrate that matter is conserved during a physical change?(1 point)

A) Find the mass of an apple. Cut the apple and remove the core. Find the mass of the remaining apple.
B) Find the mass of a raw egg. Cook the egg. Find the mass of the cooked egg.********
C) Find the mass of a cup of water. Boil the water. Find the mass of the water that remains.
D) Find the mass of a piece of ice. Let the ice melt. Find the mass of the liquid water.

10) One molecule of bromine (Br2) and two molecules of potassium chloride (KCl) combine in a reaction. How many atoms are in the products?(1 point)

A) two******
B) four
C) three
D) six

11) Use the unbalanced chemical equation to answer the question.

2NaHCO3 → Na2CO3 + CO2

What can be added to the products to balance the equation? (1 point)

A) CH2OH****
B) H2O
C) H2
D) O2

12) The chemical formula for phosphorus trichloride is PCl3. In one to two sentences, explain how you would build a ball-and-stick model of phosphorus trichloride. Include a description of the parts of the model.(2 points)

13) Copper (Cu) reacts with sulfur (S) to form copper sulfide as shown in the chemical equation. A scientist adds 4 grams of Cu to 2 grams of S to start the reaction. At the end of the experiment, she has 6 grams of product. In one to two sentences, explain what would happen if the scientist increased the amount of copper to 6 grams, and why. (1 point)

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  1. 1. yes
    2. yes
    3. Krypton is a noble gas, no way !

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    Damon
  2. 4. yes (check the halogens by the way ( F, Cl Br .... Yb))

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    Damon
  3. 5. yes
    6. yes
    7. do not see picture
    8. H2O = 2+ 16 = 18 grams/ mol so one mol of water produced
    so one mol of NaF
    NaF = 23 + 19 = 42 grams
    so I disagree

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    Damon
  4. 9. disagree, look for phase change, solid to liquid or liquid to gas

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    Damon
  5. 1 BR2 = 2 atoms
    2 KCl = 2 atoms
    2+2 = ?

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    Damon
  6. 5 and 6 are ok. No picture on 7.
    By the way, on the 4 answered above, Yb is not a halogen and it is not in the same column as the halogens. Yb is a rare earth and is placed at the bottom of the periodic table to save space.

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    DrBob222
  7. 11) Use the unbalanced chemical equation to answer the question.

    2NaHCO3 → Na2CO3 + CO2

    What can be added to the products to balance the equation? (1 point)

    A) CH2OH****
    B) H2O
    C) H2
    D) O2
    ====================================
    2NaHCO3 → Na2CO3 + CO2
    need 2 H atoms
    Have 6 O left and 5 O right, so need an O atom
    H2 + O = ??????

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    Damon
  8. 10. Br2 + KCl --> No reaction. So in the solution you will have 2 atoms of Br, two K ions and 2 Cl ions. So 2 atoms left is the correct answer.

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    DrBob222
  9. For #7
    Observation # Before Reaction During/After Reaction
    1 mass=30 grams mass= 42 grams
    2 atoms of H =5 atoms of H = 5
    3 no gas gas present
    4 two types of molecules three types of molecules

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  10. 12. If you will Google "PCl3 ball and stick model" you can find two or three pictures on the web that will answer this question for you. I found a couple of sites yesterday doing that.
    13. First you didn't show the reaction between Cu and S. I suspect that if you had it would have been wrong. I think you want the answer to be that one of these reagents is the limiting reagent; therefore, no more copper sulfide can be produced.
    The correct equation is 2Cu + S ==> Cu2S

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    DrBob222

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