1. hydrogen sulfide
2. hydrogen sulfate
3. ammonium sulfide
4. ammonium sulfate

Correct Answer Number: 1

Explanation: Only two different kinds of atoms make up a binary compound. See Ref. Table E. Hydrogen sulfate has 3 kinds of atoms (H, S, O). Ammonium sulfate has 3 kinds (N, H, S). Ammonium sulfate has 4 kinds (N, H, S, O).

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1. NaClO
2. Na₂ClO
3. Na₂C₂O₄
4. NaC₂H₃O₂

Correct Answer Number: 3

Explanation: The symbol for the first part of the formula, sodium, is Na. Go to Ref. Table E and find oxalate: C₂O₄. Notice the ion has a charge of -2. Two Na⁺ ions are needed to cancel out the -2 charge.

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1. 9
2. 7
3. 5
4. 4

Correct Answer Number: 1

Explanation: 4Al + 3O₂ = 2Al₂O₃. Coefficients are the numbers in front of the element symbols. Add 4 + 3 + 2 to get 9.

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1. PO
2. PO₂
3. P₂O₅
4. P₈O₂₀v

Correct Answer Number: 3

Explanation: Take P₄O₁₀ and reduce it to the smallest whole number ratio of atoms. In math this would be called reducing to lowest terms. P₄O₁₀ reduced by 2 equals P₂O₅.

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1. potassium chloride
2. ammonium chloride
3. potassium chlorate
4. ammonium chlorate

Correct Answer Number: 1

Explanation: Only two different kinds of atoms make up a binary compound. See Ref. Table E. Potassium chloride has K atoms and Cl atoms. All other choices have 3 kinds of atoms.

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1. NO
2. N₂O
3. NO₂
4. N₂O₃

Correct Answer Number: 2

Explanation: The oxidation number for Oxygen (O) is -2 and the oxidation number for Nitrogen (1) is +1. Since this is a compound, the oxidation numbers of the atoms in the compound must equal zero. In N₂O, note how N (2)( +1) or a +2 charge will cancel out the -2 charge of one oxygen ion.

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1. 8
2. 13
3. 21
4. 27

Correct Answer Number: 3

Explanation: Cu=1; S=1; O=4; H=10; O=5 for a total of 21 atoms.

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1. 138 g
2. 106 g
3. 99 g
4. 67 g

Correct Answer Number: 1

Explanation: Find the formula mass in grams. K =39 x 2 = 78 g; C =12 x 1 = 12 g; O =16 x 3 = 48 g. Total is 78 + 12 + 48 or 138 g. See also question #24, this topic.

1. 58.9
2. 118
3. 6.02 x 10²³
4. 1.2 x 10²⁴

Correct Answer Number: 4

Explanation: By definition one mole is 6.02 x 10²³ atoms. Two moles is twice that amount or 12.04 x 10²³ atoms or 1.2 x 10²⁴. (Do not forget to move the decimal). Answer is 1.2 x 10²⁴ atoms. See also Table A if you forget Avogadro's number.

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1. 20%
2. 40%
3. 50%
4. 60%

Correct Answer Number: 2

Explanation: Solve the problem by first finding the ratio of the mass of oxygen to the mass of the compound; then multiply by 100. MgO has a mass of 24 + 16.
Percent by mass of O = 16 / 40.
Now reduce to lowest terms: 2 / 5 or .4 and multiply by 100. Answer is 40%.
16 / 40 x 100% = 40%

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1. 1 mole of solute dissolved in 1 liter of solution?
2. 2 moles of solute dissolved in 3 liters of solution?
3. 6 moles of solute dissolved in 4 liters of solution?
4. 4 moles of solute dissolved in 8 liters of solution?

Correct Answer Number: 3

Explanation: Find the molarity ( moles of solute/liter of solution) for each answer.
#1) 1 mole / 1 liter or 1 M.        #2) 2 moles / 3 liters or 0.67 M.
#3) 6 moles / 4 liters or 1.5 M.       #4) 4 moles / 8 liters or 0.5 M.
Ans. #3 (1.5 M. ) is the most concentrated.

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1. 1.5 moles
2. 2.00 moles
3. 6.02 moles
4. 9.03 moles

Correct Answer Number: 1

Explanation: Divide 9.03 x 10²³ by 6.02 x 10²³ to find the number of moles of hydrogen gas.
9.02 / 6.02 = 1.5 moles (remember the numerator and denominator each contain 10 to the 23, so this cancels out. 1 mole equals 6.02 x 10²³ molecules).

1. CH
2. CH₂
3. CH₃
4. CH₄

Correct Answer Number: 2

Explanation: Step 1: change percent to grams.
Step 2: find out how many moles you have of C and H by:    86 g / 12 g per mole of C = 7 moles of C;   14 / 1 g per mole H = 14 moles of H.
Step 3: find the ratio of moles of C and H to each other: 14 / 7 is 2.
In other words there are 2 H moles for every C mole or CH₂. This is the empirical formula.

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1. 2.5
2. 5.0
3. 10
4. 20

Correct Answer Number: 3

Explanation: Molarity = moles of solute / volume of solution (L).
Change the formula to find moles.
Moles = molarity x volume of solution (L) or 2.0 M x 5.0 L = 10 moles of H₂SO₄

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1. 22 g
2. 44 g
3. 66 g
4. 88 g

Correct Answer Number: 1

Explanation: 1 mole of CO₂ has a formula mass of 44 grams and contains 1 mole of molecules (6.02 x 10²³). You are given 3 x 10 ²³2 equals 1/2 the mass of 1 mole of CO₂ or
1/2 x 44 = 22 g.

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1. 6.89%
2. 14.5%
3. 26.1%
4. 62.9%

Correct Answer Number: 4

Explanation: One mole of the hydrate given has a mass of 286. The 10 water moles are part of the hydrate. The water has a mass of 18 g x 10 or 180 g.
Percent of water = 180g (water mass) / 286 (mass of compound) x 100% = 62.9%

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1. 22.4 L Ar
2. 28.0 L of N₂
3. 32. 0 L of H₂
4. 44.8 L of He

Correct Answer Number: 3

Explanation: At the same temperature and pressure, equal volumes of gases have an equal (the same) number of molecules. This is known as Avogadro' hypothesis.

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1. 1.00 M
2. 2.00 M
3. 3.00 M
4. 4.00 M

Correct Answer Number: 2

Explanation: Molarity = step 1: find the moles of solute using the formula:
mass of solute (g) divided by formula mass of solute
Step 2: divide the moles of solute by volume of solution in liters M / V.
Or if you know the moles of solute,
Molarity = moles of solute divided by volume of solution in liters . KF has a formula mass of 39 + 19 or 58 g/mole. Since 116 grams are given, 116g / 58g/mole = 2 moles of solute.
To find the Molarity, take 2 moles of solute and divide by 1 L of solution.
2 moles / 1 L = 2.00 M solution

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1. 113 g
2. 121 g
3. 149 g
4. 404 g

Correct Answer Number: 3

Explanation: Find the formula mass in grams.     N =14 x 3 = 42 g;    H =1 x 4 x 3 = 12 g;    P=31 x 1=31;     O =16 x 4 = 64 g.
Total is 42 + 12 + 31 + 64 or 149 g.
See also question #2, this topic.

1. AgF
2. Ag₂F
3. AgF₂
4. Ag₂F₂

Correct Answer Number: 1

Explanation: First change % to grams.
Next convert the grams to moles. The molecular mass of Ag is 108 g/mol;    molecular mass of F is 19 g/mol.
85 g Ag / 108 g mol = 0.79 moles       15 g F / 19 g mol = 0.79 moles
Or the whole number ratio is 0.79 / 0.79 = 1 In other words, 1 Ag mole for each 1 F mole.

1. 2 moles
2. 2 atoms
3. 2 grams
4. 2 molecules

Correct Answer Number: 1

Explanation: The number of moles in a balanced equation is shown by the coefficients. Hint: when there is no coefficient (the number in front of the compound), the number 1 is understood. 1 mole of CH₄ reacts with 2 moles of 0₂.