Q: Calculate the number of phosphorus atoms in $$2.63\ \mathrm{g} of $$phosphorus pentabromide ($$\mathrm{PBr}_5). $$Also, calculate the mass in grams of bromine in $$3.28 \times 10$$^{21}$$ molecules of $$\mathrm{PBr}_5$$.

$$8.644 \times 10$$^{21}$$ atoms P, 0.752$$\ \mathrm{g}$$ Br

Q: Calculate the charge-to-mass ratio in $$\mathrm{C/kg} of an $$alpha particle, $$^4\mathrm{He}^{2+}$$, that has a mass of $$4.00151$$ amu.

$$4.82 \times 10^7$\ \mathrm{C/kg}$$

Q: Phosphorous-32 is a radioactive isotope of phosphorous and undergoes a beta decay to yield sulfur-32. If the two isotopes are to be differentiated using a mass spectrometer, what should be the precision of the mass spectrometer that is able to differentiate between the two?

$$2.306 \times 10$$^{-27}$$\ \mathrm{g}$$

Question 1

A sample contains $$1.85 	imes 10$$^{-3}$$ moles of a hormone and weighs 0.581$ grams. Calculate the molar mass of the hormone.

Accepted Answer

$$314\ \mathrm{g/mol}$$

Question 2

Calculate the number of phosphorus atoms in $$2.63\ \mathrm{g} of $$phosphorus pentabromide ($$\mathrm{PBr}_5). $$Also, calculate the mass in grams of bromine in $$3.28 	imes 10$$^{21}$$ molecules of $$\mathrm{PBr}_5$$.

Accepted Answer

$$8.644 	imes 10$$^{21}$$ atoms P, 0.752$$\ \mathrm{g}$$ Br

Question 3

At equilibrium, the decomposition reaction $$2\ \mathrm{NaNO}_3\ (s) \rightarrow 2\ \mathrm{NaNO}_2\ (s) + \mathrm{O}_2\ (g)$$ has $$2.38\ \mathrm{g}$$ $$\mathrm{NaNO}_3$$, $$3.92\ \mathrm{g}$$ $$\mathrm{NaNO}_2$$, and $$1.29\ \mathrm{g}$$ $$\mathrm{O}_2. $$How much in grams of $$\mathrm{NaNO}_3$$ was there originally if it is the only substance at the start of the reaction?

Accepted Answer

$$7.59\ \mathrm{g}$$

Question 4

Identify the number of Al, S, and O atoms in the coagulating agent aluminum sulfate $$\mathrm{Al}_2(\mathrm{SO}_4)_3.$$

Accepted Answer

Al: 2, S: 3, O: 12

Question 5

Choose from the following statements which are inconsistent with the implications and postulates of Dalton's atomic theory:
I. Two oxygen atoms combine with one nitrogen atom to form a molecule of nitrogen dioxide.
II. One lithium atom can have a mass of 6 amu while another can have a mass of 7 amu.
III. Atoms are the smallest particles of all matter.
IV. Atoms can be created.
V. Atoms of a compound are fixed and cannot rearrange.

Accepted Answer

II, IV, and V

Question 6

Find the sulfur to fluorine ratio by mass in $$\mathrm{SF}_2$$ given that $$\mathrm{NS}_2$$ has a $$2.29$$ ratio of sulfur to nitrogen and $$\mathrm{NF}_3$$ has a $$4.07$$ ratio of fluorine to nitrogen.

Accepted Answer

$$3.65$$

Question 7

Calculate the charge-to-mass ratio in $$\mathrm{C/kg} of an $$alpha particle, $$^4\mathrm{He}^{2+}$$, that has a mass of $$4.00151$$ amu.

Accepted Answer

$$4.82 	imes 10^7$\ \mathrm{C/kg}$$

Question 8

Phosphorous-32 is a radioactive isotope of phosphorous and undergoes a beta decay to yield sulfur-32. If the two isotopes are to be differentiated using a mass spectrometer, what should be the precision of the mass spectrometer that is able to differentiate between the two?

Accepted Answer

$$2.306 	imes 10$$^{-27}$$\ \mathrm{g}$$

Question 9

Select the correct empirical formula for a substance with $$11.34$$ mol C, $$11.34$$ mol H, and $$5.67$$ mol O.

Accepted Answer

$$\mathrm{C}_2\mathrm{H}_2\mathrm{O}$$

Question 10

The empirical formula of a compound is $$\mathrm{C}_{10}\mathrm{H}_{13}\mathrm{NO}. $$Provide the molecular formula for $$\mathrm{C}_{10}\mathrm{H}_{13}\mathrm{NO} if $$its molar mass is $$326.432\ \mathrm{g/mol}.$$

Accepted Answer

$$\mathrm{C}_{30}\mathrm{H}_{39}\mathrm{N}_3\mathrm{O}_3$$

Question 11

An unknown compound consists of C, H, and N. When $$0.227\ \mathrm{g} of $$the compound is ignited, it gives off $$0.6581\ \mathrm{g} of$$ $$\mathrm{CO}_2$$ and $$0.1122\ \mathrm{g} of$$ $$\mathrm{H}_2\mathrm{O}. $$Determine its empirical formula and molecular formula if its molar mass is $$273.33\ \mathrm{g/mol}.$$

Accepted Answer

empirical formula: $$\mathrm{C}_6\mathrm{H}_5\mathrm{N}_3$$; molecular formula: $$\mathrm{C}_{18}\mathrm{H}_{15}\mathrm{N}_9$$

Question 12

Tellurium forms similar compounds as sulfur. Give the name of the following ion formed by tellurium: $$\mathrm{TeO}_3$$^{2-}$$.

Accepted Answer

tellurite ion

Question 13

Identify the names of the positive ions involved in each of the following compounds:
A) $$\mathrm{MgO}
B$$) $$\mathrm{K}_2\mathrm{SO}_4
C$$) $$\mathrm{NaBrO}_4
D$$) $$\mathrm{Co(NO_3$)_2}
E$$) $$\mathrm{Mn(OH)_2}$$

Accepted Answer

A) Magnesium oxide, B) Potassium sulfate, C) Sodium perbromate, D) Cobalt(II) nitrate, E) Manganese(II) hydroxide

Question 14

Provide the name and formula of the compound formed by magnesium and iodine.

Accepted Answer

$$\mathrm{MgI}_2$$, magnesium iodide

Question 15

Identify the formula of gallium nitrate pentahydrate.

Accepted Answer

$$\mathrm{Ga(NO_3$)_3} \cdot 5\ \mathrm{H_2O}$$

Question 16

Identify which pairing is incorrect:
a. $$\mathrm{HBr}$$, hydrobromide acid
b. $$\mathrm{H_2CrO_4}$$, chromic acid
c. $$\mathrm{H_2PO_3}$$, phosphoric acid
d. $$\mathrm{HCl}$$, hydrochloric acid

Accepted Answer

b and c

Question 17

Label the types of molecules as the following:
(i) Monoatomic element
(ii) Diatomic element
(iii) Polyatomic element
(iv) Molecular compound
(v) Ionic compound

a) Chlorine
b) $$\mathrm{C$$_{12}$$H_{22}O_6$}
c) $$Copper
d) Oxygen
e) $$\mathrm{NH_4Cl}
f) $$Argon

Accepted Answer

a) (ii), b) (iv), c) (i), d) (ii), e) (v), f) (i)

Question 18

Balance the following chemical equation:
$$\mathrm{Co(NO_3$)_3(aq)} + \mathrm{(NH_4$)_2CO_3(aq)} \rightarrow \mathrm{Co_2$(CO_3$)_3(s)} + \mathrm{NH_4NO_3(aq)}$$

Accepted Answer

$$2\ \mathrm{Co(NO_3$)_3(aq)} + 3\ \mathrm{(NH_4$)_2CO_3(aq)} \rightarrow \mathrm{Co_2$(CO_3$)_3(s)} + 6\ \mathrm{NH_4NO_3(aq)}$$

Question 19

Rubidium metal reacts with iodine gas as described in the following equation:
$$2\mathrm{Rb}(s) + \mathrm{I}_2(g) \rightarrow 2\mathrm{RbI}(s)$$
Initially, the reaction mixture contains $$45.2\ \mathrm{g} Rb $$and $$92.3\ \mathrm{g}$$ $$\mathrm{I}_2. $$How many grams of the excess reactant remain after the reaction has occurred completely?

Accepted Answer

$$8.48\ \mathrm{g} Rb$$

Question 20

Ethyl chloride ($$\mathrm{C_2H_5Cl}) is $$produced by the reaction of chlorine ($$\mathrm{Cl_2$}) $$and ethane ($$\mathrm{C_2H_6}). $$However, minor products such as $$\mathrm{C_2H_4Cl_2}$$ are also produced in minuscule amounts. This minor product reduces the yield of $$\mathrm{C_2H_5Cl}.
A) $$Assuming that only $$\mathrm{C_2H_5Cl}$$ and HCl is formed, calculate the theoretical yield when $$172.8\ \mathrm{g} of$$ $$\mathrm{C_2H_6} is $$reacted with $$402.6\ \mathrm{g} of$$ $$\mathrm{Cl_2$}.
B) If $$the reaction produces $$153\ \mathrm{g} of$$ $$\mathrm{C_2H_5Cl}$$, calculate the percent yield of $$\mathrm{C_2H_5Cl}.$$

Accepted Answer

$$310.12\ \mathrm{g},\ 71.76\%$$

Question 21

Identify the element X in $$\mathrm{XBr}_4$$ given that it is $$96.4\% Br by $$mass.

Accepted Answer

C

Question 22

Is $$\mathrm{H_3CCHCHCH_2CH_3} an $$alkane, alkene, or alkyne?

Accepted Answer

alkene

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