Question

true/false. write t if the statement is true and f if the statement is false.

1. mass is used as a method of counting atoms.
2. avogadros number is 6.022×10²³.
3. one mole of copper atoms is 6.022×10²³ copper atoms.
4. two moles of cobalt atoms have a mass of 117.87 grams.
5. one mole of co₂ gas contains 1 mole of carbon atoms and 2 moles of oxygen atoms.
6. one mole of water contains 6.022×10²³ hydrogen atoms.
7. the molar mass of a compound serves as a conversion factor between grams and moles.
8. the correct formula for calculating mass percent of x in compound xy is:

\frac{mass of x in a sample of the compound}{mass of y in a sample of the compound}=mass % x

1. c₂h₆o₃ could be an empirical formula.
2. an empirical formula gives the specific number of each type of atom in a molecule.
3. the empirical formula for c₆h₆ is c₃h₃.
4. the empirical formula mass is 18.0 and the molecular formula mass is 90, therefore n = 5.

multiple choice. choose the one alternative that best completes the statement or answers the question.

1. which of the following statements about the mole is false?

a) a mole of an element corresponds to one avogadro number of atoms.
b) the size of a mole of atoms has a reasonable mass.
c) one mole of an element has a mass equal to its atomic mass expressed in grams.
d) one mole of water contains 1/2 mole of oxygen atoms.
e) none of the above

1. how many atoms are in 1.50 moles of fluorine gas?

a) 18.98
b) 6.022×10²³
c) 9.03×10²³
d) 1.81×10²⁴
e) none of the above

Explanation:

Step1: Recall atomic counting method

Mass is not used as a method of counting atoms directly. Moles are used for counting atoms. So, 1) is F.

Step2: Know Avogadro's number

Avogadro's number is $6.022\times 10^{23}$, so 2) is T.

Step3: Understand mole - atom relationship

One mole of any substance contains $6.022\times 10^{23}$ entities. So one mole of copper atoms is $6.022\times 10^{23}$ copper atoms, 3) is T.

Step4: Calculate mass of cobalt

The molar mass of cobalt (Co) is approximately 58.93 g/mol. Two moles of cobalt atoms have a mass of $2\times58.93 = 117.86\approx117.87$ grams, 4) is T.

Step5: Analyze CO₂ composition

In one mole of $CO_{2}$, there is 1 mole of carbon atoms and 2 moles of oxygen atoms according to the formula, 5) is T.

Step6: Analyze water composition

One mole of water ($H_{2}O$) contains 2 moles of hydrogen atoms, so it contains $2\times6.022\times 10^{23}=1.2044\times 10^{24}$ hydrogen atoms. So 6) is F.

Step7: Recall molar - mass conversion

The molar mass of a compound is used to convert between grams and moles ($n=\frac{m}{M}$), 7) is T.

Step8: Recall mass - percent formula

The formula for mass percent of X in compound XY is $\frac{\text{Mass of X in a sample of the compound}}{\text{Total mass of the sample of the compound}}\times 100\%$, not as given. So 8) is F.

Step9: Recall empirical - formula concept

$C_{2}H_{6}O_{3}$ could be an empirical formula if the ratio of atoms cannot be further simplified, 9) is T.

Step10: Recall empirical - formula definition

An empirical formula gives the simplest whole - number ratio of atoms in a molecule, not the specific number of each type of atom. So 10) is F.

Step11: Simplify molecular formula

The empirical formula for $C_{6}H_{6}$ is CH (divide subscripts by 6), not $C_{3}H_{3}$. So 11) is F.

Step12: Calculate n for formula

If the empirical - formula mass is 18.0 and the molecular - formula mass is 90, then $n=\frac{\text{Molecular - formula mass}}{\text{Empirical - formula mass}}=\frac{90}{18}=5$. So 12) is T.

Step13: Analyze mole statements

In one mole of water ($H_{2}O$), there is 1 mole of oxygen atoms. So statement D in 13) is false. The answer for 13) is D.

Step14: Calculate number of atoms

One mole of any substance contains $6.022\times 10^{23}$ entities. For 1.50 moles of fluorine gas ($F_{2}$), the number of atoms is $1.50\times2\times6.022\times 10^{23}=1.8066\times 10^{24}\approx1.81\times 10^{24}$. The answer for 14) is D.

Answer:

1. F
2. T
3. T
4. T
5. T
6. F
7. T
8. F
9. T
10. F
11. F
12. T
13. D. One mole of water contains 1/2 mole of oxygen atoms
14. D. $1.81\times 10^{24}$