Experience 2: Chemical Calculations

Mole ratios from balanced equations may be used to solve problems with other units such as numbers of

representative particles

Mole ratios from balanced equations may be used to solve problems with other units such as numbers of representative particles and____ of gases at STP

volumes

The ____from the balanced equation are used to write conversion factors called mole ratios.

coefficients

The coefficients from the balanced equation are used

to write conversion factors called

mole ratios

These conversion factors are used to calculate the numbers of moles of ____ from a given number of moles of reactants.

products

These conversion factors are used to calculate the numbers of moles of products from a given number of moles of

reactants

In mass-mass calculations, the molar mass is used to convert mass to

moles

In mass-mass calculations, the molar mass is used to convert mass to moles.

AT

The mole ratio 2 mol HF/1 mol SnF2 can be used to determine the mass of SnF2 produced according to the equation: Sn(s) + 2HF(g) ----> SnF2(s) + H2(g)

NT

In a volume-volume problem, the 22.4 L/mol factors always cancel out.

AT

In stoichiometric problems, volume is expressed in terms of liters.

NT

For a mass-mole problem, the first conversion from mass to moles is skipped

NT

For a mass-mass problem, the first conversion is from moles to mass

NT

Because mole ratios from balanced equations are exact numbers, they do not enter into the determination of significant figures.

AT

How many liters of carbon monoxide (at STP) are needed to react with 4.8 g of oxygen gas to produce carbon dioxide?

6.7 L

What mass of ammonia, NH3, is necessary to react with 2.1 x 1024 molecules of oxygen in the following reaction? 4NH3(g) + 7O2(g) -----> 6H2O(g) + 4NO2(g)

33.9 grams

Is it essential to have a balanced equation prior performing calculations involving amounts of reactants and products?

True

If you know the number of moles of one substance in a reaction, you need more information than the balanced chemical equation to determine the number of moles of all the other substances in the reaction

False

The coefficients from a balanced chemical equation are used to write conversion factors called

mole ratios

2K(s) + Cl2(g) ---> 2KCl(s)

Laboratory balances are used to measure moles of substances directly

False

The amount of a substance is usually determined by measuring its mass in

grams

If a sample is measured in grams, molar mass can be used to convert the mass to moles.

True

Stoichiometric calculations can be expanded to include any unit of measurement that is related to the mole.

True

In any problem relating to stoichiometric calculations, the given quantity is first converted to

moles

Knowledge about what products are produced in a chemical reaction is obtained by:

A. Inspecting the chemical equation
B. Balancing the chemical equation
C. Laboratory analysis
D. Writing a word equation

C. Laboratory analysis

Which observation does NOT indicate that a chemical reaction has occurred?:

A. Formation of a precipitate
B. Production of a gas
C. Evolution of heat and light
D. Change in total mass of substances

D. Change in total mass of substances

A solid produced by a chemical reaction in solution that separates from the solution is called:

A. A precipitate
B. A reactant
C. A molecule
D. The mass of the product

A. A precipitate

After the correct formula for a reactant in an equation has been written, the:

A. Subscripts are adjusted to balance the equation
B. Formula should not be changed
C. Same formula must appear as the product
D. Symbols in the formula must not appear on the product side of the equation

B. Formula should not be changed

What is the small whole number that appears in front of a formula in a chemical reaction?:

A. A subscript
B. A superscript
C. A ratio
D. A coefficient

D. A coefficient

To balance a chemical equation, it may be necessary to adjust the:

A. Coefficients
B. Subscripts
C. Formulas of the products
D. Number of products

A. Coefficients

According to the law of conservation of mass, the total mass of the reacting substances is:

A. Always more than the total mass of the proudcts
B. Always less than the total mass of the products
C. Sometimes more and sometimes less than the total mass of the products
D. Always equal to the total mass of products

D. Always equal to the total mass of the products

A chemical equation is balanced when the:

A. Coefficients of the reactants equal the coefficients of the products
B. Same number of each kind of atom appears in the reactants and in the products
C. Products and reactants are the same chemicals
D. Subscripts of the reactants equal the subscripts of the products

B. Same number of each kind of atom appears in the reactants and in the products

How would oxygen be represented in the formula equation for the reaction of methane and oxygen to yield carbon dioxide and water?

A. Oxygen
B. O
C. O2
D. 03

C. O2

Which of the following is a formula equation for the formation of carbon dioxide from carbon and oxygen?:

A. Carbon plus oxygen yields carbon dioxide
B. C + O2 --> CO2
C. CO2 --> C + O2
D. 2C + O --> CO2

B. C + O2 --> CO2

                        For the formula equation 2Mg + O2 --> 2MgO, the word equation would begin:

A. Manganese plus oxygen…
B. Molybdenum plus oxygen…
C. Magnesium plus oxygen…
D. Heat plus oxygen…

                        C. Magnesium plus oxygen                          

                        In an equation, the symbol for a substance in water solution is followed by:

A. (l)
B. (g)
C. (aq)
D. (s)

                        A. (l)                          

                        A chemical formula written over the arrow in a chemical equation signifies:

A. A byproduct
B. The formation of a gas
C. A catalyst for the reaction
D. An impurity

                        C. A catalyst for the reaction                          

                        Which coefficients correctly balance the formula equation NH4NO2(s)-->N2(g)+H2O9(l)?:

A. 1, 2, 2
B. 1, 1, 2
C. 2, 1, 1
D. 2, 2, 2

                        B. 1, 1, 2                          

                        After the first steps in writing an equation, the equation is balanced by:

A. Adjusting the subscripts to the formula(s)
B. Adjusting coefficients to the smallest whole-number ratio
C. Changing the products formed
D. Making the number of reactants equal to the number of products

                        B. Adjusting coefficients to the smallest whole-number ratio                          

Mole ratios from balanced equations may be used to solve problems with other units such as numbers of ______ and _____ of gases at STP

Representaive particles; volumes

The _________ from the balanced equation are used to write conversion factors called ___________.

Coefficients; mole ratios

These conversion factors are used to calculate the number of moles of _________ from a given number of moles of __________.

Product; reactant

In mass-mass calculations, the molar mass is used to convert mass to ______.

Moles

In mass-mass calculations, the molar mad is used to convert mass to moles.

NT, AT, ST

AT

The mole ratio 2 mol HF/1 mol SnF₂ can be used to determine the mass of SnF₂ produced according to the equation:

Sn(s) + 2HF(g) ——-> SnF₂ + H₂(g)

NT, AT, ST

NT; you can't use that ratio because the equation is not balanced

In a volume-volume problem, the 22.4 L/mol factors always cancel out.

NT, AT, ST

AT

In stoichiometric problems, volume is expressed in terms of liters.

NT, AT, ST

ST; volume could also be expressed in moles or cubic meters

For a mass-mole problem, the first conversion from mass to moles is skipped.

NT, AT, ST

NT; you must convert mass to moles for stoichiometry to work in mass-mole problems (you can skip the step in volume-mole problems)

For a mass-mass problem, the first conversion is from moles to mass.

NT, AT, ST

NT; it is from mass to moles

Because mole ratios from balanced equations are exact numbers, they do not enter into the determination of significant figures.

NT, AT, ST

AT

Moles 0₂ —> grams O₂

Mol * 32.0g/ mol

Liters SO₂ —> grams SO₂ at STP

Liters mol/22.4L 64.1g/mol

Molecules He —> liters He(g) at STP

Molecules mol/(6.0210^23) * 22.4L/mol

Grams Sn —> molecules Sn

Grams mol/119g (6.02*10^23 molecules)/ mol

Molecules H₂O —> grams H₂O

Molecules mol/ (6.0210^23 molecules) * 18.0g/mol

How many liters of carbon monoxide at STP are needed to react with 4.8 g of oxygen gas to produce carbon dioxide?

2CO(g) + O₂(g) —> 2CO₂(g)

6.7 liters of CO

What mass of ammonia, NH3, is necessary to react with 2.1*10^24 molecules of oxygen in the following reaction?

4NH₃(g)+7O₂(g) —> 6H₂O(g) + 4NO₂(g)

33.9 grams of NH3