Topics include: mole calculations, % composition by mass, mole to mole problems using equations, calculating average atomic mass and formula mass, empirical versus molecular formula.
June 2024
1.
SOLUTION
We need to look at the Periodic Table to find the mass of each element. C= 12 H=1 N=14 O=16
Then we need to multiply the mass of each element by the number of atoms in the formula (represented by the subscript)
9*12+11*1+1*14+2*16
Answer 4
2.
SOLUTION
According to the Law of Conservation of Mass, mass of reactants must be equal to the mass of the products.
Mass of CO+O2 = Mass of CO2
Mass of O2 + 5.6g = 8.8g, Mass of O2 = 8.8-5.6 = 3.2g Answer 3
January 2024
3.
SOLUTION
We can calculate the gram-formula mass by looking up the mass of each element on the Periodic Table and multiplying it by the number of atoms in the formula (subscripts). (NO3)2 means there are 2 atoms of N and 6 atoms of O.
Mg=1*24 = 24, N =14*2= 28, O=16*6 = 96. Now, we can sum all the numbers to get 148g/mol , answer 3.
August 2023
4.
SOLUTION
According to the Law of Conservation of Mass, mass of reactants must be equal to the mass of the products.
Mass of Mg+N2 = Mass of Mg3N2
14.58+5.6= 20.18 Answer 3
June 2023
5.
SOLUTION
To calculate the average atomic mass of an element, we take the atomic mass of each isotope and multiply by percent abundance in the decimal form ( divide by 100).
Average atomic mass of silver = (106.905u)(51.8%) + (108.905 u)(48.2%)
Answer: Choice 2 is the correct answer.
6.
SOLUTION
Table T on the Reference Table shows the formula for mole calculations. number of moles = given mass/ gram-formula mass.
Number of moles. = 78.8g/84.3g/mol = 0.935moles
Answer: 2
January 2023
7.
SOLUTION
o calculate the average atomic mass of an element, we take the atomic mass of each isotope and multiply by percent abundance in the decimal form ( divide by 100).
Average atomic mass of rhenium = (184.95 u)(0.3740) + (186.96 u)(0.6260)
Answer: Choice 2 is the correct answer.
8.
SOLUTION
According to the conservation of mass, mass of the reactants must be equal to the mass of products. We have all the masses except for KCl. 24.51g = 9.60g + x, x = 14.91 g
Answer: choice 2 is correct
9.
SOLUTION
We need to make sure atoms of each element are balanced on each side. In answer choice 4, there are 3 Ti on both sides, 4 Al on both sides and 6 O on both sides.
Answer: Choice 4 is correct.
10.
SOLUTION
Gram formula mass (or molar mass) gives us the number of grams per 1 mol of compound. Looking at the Periodic Table, bromine has a molar mass of 79.904g. Br2 mass would be: 2* 79.904g = 159.8 g which is the correct answer
Answer: 4
REGENTS CHEMISTRY COURSE and other topics practice.