Q: Which is an exact number?

$$6.02 \times 10$$^{23}$$ - Avogadro's number

Question 1

A liquid has a density of $$6.75\ \mathrm{g/cm^3$}. $$How many kilograms are in $$11.1\ \mathrm{L} of $$this substance?

Accepted Answer

$$74.9\ \mathrm{kg}$$

Question 2

The prefix 'milli-' before a unit of measure is associated with a multiplier value of:

Accepted Answer

$$0.001$$

Question 3

The SI unit for temperature is:

Accepted Answer

Kelvin ($$K)$$

Question 4

The number $$0.00723$$ has how many significant figures?

Accepted Answer

$$4$$

Question 5

Avogadro's number is $$6.02 	imes 10$$^{23}$$. How many atoms of potassium (K$) are in 3.2$ grams of potassium (use 39.0$$\ \mathrm{g}$$ as its molar mass)?

Accepted Answer

$$4.92 	imes 10$$^{22}$$

Question 6

Carbon tetrachloride, $$\mathrm{$$CCl_4$$}$$, was once used as a dry-cleaning fluid. If you have $$11.4$$ moles of $$\mathrm{$$CCl_4$$}$$, how many moles of Cl does it contain?

Accepted Answer

$$45.6$$

Question 7

The atomic number of iron, Fe, is $$26. $$How many electrons does an atom of iron have?

Accepted Answer

$$26$$

Question 8

The atomic number of tin, Sn, is $$50. $$Which of the following is the most likely number of neutrons for a tin atom to have?

Accepted Answer

$$68$$

Question 9

Aspirin has the formula $$\mathrm{C_9H_8O_4}. If $$the atomic masses of C, H, and O are respectively $$12.0$$, $$1.00$$, and $$16.0$$, what is the molar mass of aspirin?

Accepted Answer

$$180.0\ \mathrm{g/mol}$$

Question 10

Ethanol has the chemical formula $$\mathrm{C_2H_6O}. $$What are its percent compositions of C, H, and O, respectively? For your work, use the following masses: C = $$12.0$$, H = $$1.00$$, O = $$16.0 ($$all in $$\mathrm{g/mol}).$$

Accepted Answer

$$52.2\% C$$, $$13.0\% H$$, $$34.8\% O$$

Question 11

What is the molar mass/molecular weight of ethanol (use the data from problem 10 above)?

Accepted Answer

$$46.0\ \mathrm{g/mol}$$

Question 12

A chemical compound has the empirical formula $$\mathrm{HBN}. $$Its molecular weight is $$81.0\ \mathrm{g/mol}. $$What is its molecular formula? (use B = $$11.0$$, H = $$1.00$$, N = $$14.0)$$

Accepted Answer

$$\mathrm{H_3B_3N_3}$$

Question 13

As mentioned in class Wednesday, chloroform ($$\mathrm{$$CHCl_3$$}) $$and tetrachloroethylene ($$\mathrm{C_2Cl_4}) $$were once used (respectively) as:

Accepted Answer

an anesthetic, a dry-cleaning fluid

Question 14

Which is an exact number?

Accepted Answer

$$6.02 	imes 10$$^{23}$$ - Avogadro's number

Question 15

A flask contains $$26.2$$ moles of hydrogen ($$52.4\ \mathrm{g}) $$and $$13.1$$ moles of oxygen ($$419.2\ \mathrm{g}). A $$spark is provided, and the two are completely consumed, forming water, $$\mathrm{H_2O}. $$About how many grams of water does the flask contain?

Accepted Answer

$$472\ \mathrm{g}$$

Question 16

Which of the following statements about significant figures is correct?

Accepted Answer

Trailing zeros in a number with a decimal point are significant.

Question 17

Which of the following is a chemical property?

Accepted Answer

Flammability

Question 18

Which of the following best describes an isotope?

Accepted Answer

Atoms with the same number of protons but different numbers of neutrons

Question 19

Which of the following is a physical change?

Accepted Answer

Melting of ice

Question 20

Which of the following is the correct electron configuration for a neutral atom of carbon ($$Z=6$$)?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^2$$

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