Science/Chemistry

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?
The model should show 27 protons and 32 neutrons.
The model should show 27 protons and 27 neutrons.
The model should show 32 protons and 59 neutrons.
The model should show 59 protons and 27 neutrons

In a molecule of lithium sulfide, there are two atoms of lithium and one atom of sulfur. Which statement about lithium sulfide is correct?
The atoms in lithium sulfide are held together by bonds.
The chemical formula for lithium sulfide is LiS2.
Both lithium and sulfur form positive ions.
A molecular model of lithium sulfide would have two spheres

Which element has the same number of valence electrons as bromine (Br)?
ytterbium (Yb)
krypton (Kr)
astatine (At)
selenium (Se)

Why are sodium (Na) and potassium (K) in the same group on the periodic table?
They have similar reactivity.
They have similar atomic weights.
They are both colorless.
They are both hard and brittle.

A student cuts some fabric into two pieces. Is this change physical or chemical?
It is a physical change because the process is reversible.
It is a physical change because there is no reaction.
It is a chemical change because the size changes.
It is a chemical change because there is no phase change.

How are chemical changes different from physical changes?
They involve heat.
They form new substances.
They include shifts in the phase of matter.
They are reversible.

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

A scientist makes several observations about a chemical reaction and records them in the table shown. Which observation contains an error?
1
4
3
2

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?
60 grams
78 grams
18 grams
42 grams

Which procedure could be used to demonstrate that matter is conserved during a physical change?
Find the mass of a cup of water. Boil the water. Find the mass of the water that remains.
Find the mass of an apple. Cut the apple and remove the core. Find the mass of the remaining apple.
Find the mass of a raw egg. Cook the egg. Find the mass of the cooked egg.
Find the mass of a piece of ice. Let the ice melt. Find the mass of the liquid water.

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

Use the unbalanced chemical equation to answer the question.

2NaHCO3 → Na2CO3 + CO2

What can be added to the products to balance the equation?
O2
H2
CH2OH
H2O

Please help me someone I need help because Jiskha keeps updating and reseting so can someone please just help me.

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  1. 58 - 27 = 32
    so yes 27 protons, 32 neutrons
    I am not going to do all these for you. I do not need the practiced but you do.
    Where is your work?

    Believe me the teachers here have complained about the new Jiska format. We are also frustrated.

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    Damon
  2. I don't see any effort on your part to answer any of these. What are your thoughts? Get out a periodic table. That will answer several just by looking at the chart.
    If you lose your post, which is easy these days, just click on load more and your post will be down the list somewhere.

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    DrBob222

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