Q: A hormone sample weighing 0.581 grams contains $$1.85 \times 10$$^{-3}$$ moles. What is the molar mass of the hormone, and which equation would you use to solve it?

Molar mass $$= \frac{0.581\ \text{g}}{1.85 \times 10$$^{-3}$$\ \text{mol}} = 314\ \text{g/mol}$$

Q: You have 2.63 g of phosphorus pentabromide ($$\text{PBr}_5). $$How many phosphorus atoms are present, and what is the mass of bromine in $$3.28 \times 10$$^{21}$$ molecules of $$\text{PBr}_5$$?

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

Q: In the decomposition reaction $$2\ \text{NaNO}_3\ (s) \rightarrow 2\ \text{NaNO}_2\ (s) + \text{O}_2\ (g)$$, if at equilibrium you have $$2.38 g $$NaNO$$_3$$, $$3.92 g $$NaNO$$_2$$, and $$1.29 g O$_2$$, what was the original mass of NaNO$$_3$$?

Original mass $$= 2.38\ \text{g} + 3.92\ \text{g} + 1.29\ \text{g} = 7.59\ \text{g}$$

Q: An alpha particle ($$^4\text{He}^{2+}) $$has a mass of $$4.00151$$ amu. What is its charge-to-mass ratio in C/kg?

$$2.41 \times 10^7$\ \text{C/kg}$$

Q: Phosphorus-32 undergoes beta decay to yield sulfur-32. If a mass spectrometer is to differentiate between these isotopes, what should be its minimum precision?

$$1.452 \times 10$$^{-26}$$\ \text{g}$$

Q: A compound contains $$11.34$$ mol C, $$11.34$$ mol H, and $$5.67$$ mol O. What is its empirical formula?

Empirical formula: $$\text{C}_2\text{H}_2\text{O}$$

Q: The empirical formula of a compound is $$\text{C}_{10}\text{H}_{13}\text{NO}$$ and its molar mass is $$326.432 g/$$mol. What is its molecular formula?

Molecular formula: $$\text{C}_{40}\text{H}_{52}\text{N}_4\text{O}_4$$

Q: A compound containing C, H, and N is combusted, producing $$0.6581 g CO$_2$$ and $$0.1122 g H$_2O $$from $$0.227 g $$sample. If its molar mass is $$273.33 g/$$mol, what are its empirical and molecular formulas?

Empirical formula: $$\text{C}_6\text{H}_5\text{N}$$; Molecular formula: $$\text{C}_{18}\text{H}_{15}\text{N}_3$$

Question 1

A hormone sample weighing 0.581 grams contains $$1.85 	imes 10$$^{-3}$$ moles. What is the molar mass of the hormone, and which equation would you use to solve it?

Accepted Answer

Molar mass $$= \frac{0.581\ 	ext{g}}{1.85 	imes 10$$^{-3}$$\ 	ext{mol}} = 314\ 	ext{g/mol}$$

Question 2

You have 2.63 g of phosphorus pentabromide ($$	ext{PBr}_5). $$How many phosphorus atoms are present, and what is the mass of bromine in $$3.28 	imes 10$$^{21}$$ molecules of $$	ext{PBr}_5$$?

Accepted Answer

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

Question 3

In the decomposition reaction $$2\ 	ext{NaNO}_3\ (s) ightarrow 2\ 	ext{NaNO}_2\ (s) + 	ext{O}_2\ (g)$$, if at equilibrium you have $$2.38 g $$NaNO$$_3$$, $$3.92 g $$NaNO$$_2$$, and $$1.29 g O$_2$$, what was the original mass of NaNO$$_3$$?

Accepted Answer

Original mass $$= 2.38\ 	ext{g} + 3.92\ 	ext{g} + 1.29\ 	ext{g} = 7.59\ 	ext{g}$$

Question 4

How many atoms of aluminum, sulfur, and oxygen are present in one formula unit of aluminum sulfate ($$	ext{Al}_2(	ext{SO}_4)_3$$)?

Accepted Answer

Al: 2, S: 3, O: 12

Question 5

Which statements are inconsistent with Dalton's atomic theory?

Accepted Answer

II, IV, and V

Question 6

Given that NS$$_2$$ has a sulfur-to-nitrogen mass ratio of $$2.29$$ and NF$$_3$$ has a fluorine-to-nitrogen mass ratio of $$4.07$$, what is the sulfur-to-fluorine ratio by mass in SF$$_2$$?

Accepted Answer

Sulfur-to-fluorine ratio $$= 3.65$$

Question 7

An alpha particle ($$^4	ext{He}^{2+}) $$has a mass of $$4.00151$$ amu. What is its charge-to-mass ratio in C/kg?

Accepted Answer

$$2.41 	imes 10^7$\ 	ext{C/kg}$$

Question 8

Phosphorus-32 undergoes beta decay to yield sulfur-32. If a mass spectrometer is to differentiate between these isotopes, what should be its minimum precision?

Accepted Answer

$$1.452 	imes 10$$^{-26}$$\ 	ext{g}$$

Question 9

A compound contains $$11.34$$ mol C, $$11.34$$ mol H, and $$5.67$$ mol O. What is its empirical formula?

Accepted Answer

Empirical formula: $$	ext{C}_2	ext{H}_2	ext{O}$$

Question 10

The empirical formula of a compound is $$	ext{C}_{10}	ext{H}_{13}	ext{NO}$$ and its molar mass is $$326.432 g/$$mol. What is its molecular formula?

Accepted Answer

Molecular formula: $$	ext{C}_{40}	ext{H}_{52}	ext{N}_4	ext{O}_4$$

Question 11

A compound containing C, H, and N is combusted, producing $$0.6581 g CO$_2$$ and $$0.1122 g H$_2O $$from $$0.227 g $$sample. If its molar mass is $$273.33 g/$$mol, what are its empirical and molecular formulas?

Accepted Answer

Empirical formula: $$	ext{C}_6	ext{H}_5	ext{N}$$; Molecular formula: $$	ext{C}_{18}	ext{H}_{15}	ext{N}_3$$

Question 12

What is the correct name for the ion $$	ext{TeO}_3$$^{2-}$$ formed by tellurium?

Accepted Answer

Tellurite ion

Question 13

Identify the names of the positive ions in the following compounds: A) MgO, B) K$$_2SO$_4$$, C) NaBrO$$_4$$, D) Co(NO$$_3$$)$$_2$$, E) Mn(OH)$$_2.$$

Accepted Answer

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

Question 14

What is the correct formula and name for the compound formed by magnesium and iodine?

Accepted Answer

MgI$$_2$$, magnesium iodide

Question 15

What is the formula for gallium nitrate pentahydrate?

Accepted Answer

Ga(NO$$_3$$)$$_3$$ · 5 H$$_2O$$

Question 16

Which acid name and formula pairing is incorrect?

Accepted Answer

HBr, hydrobromide acid

Question 17

Classify the following substances: a) Chlorine, b) C$$_{12}H$_{22}O$_6$$, c) Copper, d) Oxygen, e) NH$$_4Cl$$, f) Argon.

Accepted Answer

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

Question 18

Balance the following equation: $$	ext{Co(NO}_3)_3	ext{(aq)} + (	ext{NH}_4)_2	ext{CO}_3	ext{(aq)} ightarrow 	ext{Co}_2(	ext{CO}_3)_3	ext{(s)} + 	ext{NH}_4	ext{NO}_3	ext{(aq)}$$

Accepted Answer

$$3\ 	ext{Co(NO}_3)_3	ext{(aq)} + 2\ (	ext{NH}_4)_2	ext{CO}_3	ext{(aq)} ightarrow 2\ 	ext{Co}_2(	ext{CO}_3)_3	ext{(s)} + 4\ 	ext{NH}_4	ext{NO}_3	ext{(aq)}$$

Question 19

Rubidium reacts with iodine gas: $$2	ext{Rb}(s) + 	ext{I}_2(g) ightarrow 2	ext{RbI}(s). If $$you start with $$45.2 g Rb $$and $$92.3 g I$_2$$, how many grams of the excess reactant remain after the reaction is complete?

Accepted Answer

17.0 g Rb

Question 20

Ethane ($$	ext{C}_2	ext{H}_6) $$reacts with chlorine ($$	ext{Cl}_2) to $$produce $$	ext{C}_2	ext{H}_5	ext{Cl}$$ and HCl. If $$172.8 g of$$ $$	ext{C}_2	ext{H}_6$$ reacts with $$402.6 g of$$ $$	ext{Cl}_2$$ and produces $$153 g of$$ $$	ext{C}_2	ext{H}_5	ext{Cl}$$, what is the percent yield?

Accepted Answer

Theoretical yield: $$310.12 g$$, Percent yield: $$71.76\%$$

Question 21

In the compound XBr$$_4$$, the element X makes up $$3.6\% of $$the mass and Br makes up $$96.4\%. $$What is element X?

Accepted Answer

Si

Question 22

Is $$	ext{H}_3	ext{CCHCHCH}_2	ext{CH}_3 an $$alkane, alkene, or alkyne?

Accepted Answer

Alkene

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