Concentration
Calculate the concentration of a solution of sodium hydroxide, NaOH in mol/dm3, when 80g is dissolved in 500cm3 of water.
Relative atomic masses, Na=23, H=1, O=16
me NaOH=23+16+1= 40g
SO 40g=1 mole
Thus, 80g=2 moles
500/1000=0.5 dm3
concentration= 2 mol/0.5 dm3= 4mol/dm3
Calculate the molar mass of each compound:
Mg(NO3)2
Cr(NO3)2
Mg(NO3)2= 24.305+(2)7+6(15.999)=184.135 g
Cr(NO3)2= 51.9961+ 2(14.0067)+ 6(15.999)=176.0035 g
A compound was found to contain 32.65% Sulfur, 65.3% Oxygen and 2.04% Hydrogen. What is the empirical formula of the compound?
The first step in this problem is to change the % to grams.
32.65%→32.65g of S
65.3%→65.3g of O
2.04%→2.04g of H
2Next divide all the given masses by their molar mass.
32.65g of S/ 32gm-1 = 1.0203 moles of S
65.3g of O/ 16gm-1 = 4.08 moles of O
2.04g of H/ 1.008gm-1 = 2.024 moles of H
Then, pick the smallest answer in moles
1.0203 moles of S/ 1.0203 = 1
4.08 moles of O/1.0203 = 3.998 ≈ 4
2.024 moles of H/1.0203 = 1.984 ≈ 2
S = 1
O = 4
H = 2
H2SO4
A student preformed a chemical reaction and obtained 8.25 grams of product. According to the balanced chemical equation, the theoretical yield for this reaction is 10.00 grams. What is the percent yield of the reaction?
The percent yield is calculated by dividing the actual yield (8.25) by the theoretical yield (10.00 g) and multiplying by 100%:
percentange yield= (actual yield/ theoretical yield) x 100%
percentange yield= (8.25 g/10.00 g) x 100
percentage yield= 82.5%
How many particles are in 0.60 mol KCl?
N= n x L
N= 0.60(6.02 x 1023)
N= 3.612 x 1023 g
25.0 cm3 of 0.050 mol/dm3 sodium carbonate was completely neutralized by 20.00 cm3 od dilture hydrochloric acid. Calculate the concentration in mol/dm3 of the hydrochloric acid.
Amount of Na2CO3= 25.00(0.059)/1000=0.00125 mol
1 mol of Na2CO3 reacts with 2 mol of HCl, so the molar ratio is 1:2So, 0.00125 moles of Na2CO3 reacts with 0.00250 moles of HCl/
1 dm3=1000cm3
Volume of HCl= 20/1000=0.0200 dm3
Concentration HCl (mol/dm3)= 0.00250/0.0200=0.125 mol/dm3
How many moles are in 5 x 1024 atoms of Li? Submit your answer to the nearest whole number.
n = N/L
n = (5 x 1024 ) / (6.02 x 1023 )
n = 8.30564784053
n= 8 mol
A compound contains 88.79% oxygen (O) and 11.19% hydrogen (H). Compute the empirical formula of the compound.
Assume 100.0g of substance. We see that the percentage of each element matches the grams of each element
11.19g H
88.79g O
Convert grams of each element to moles
H: (11.19/1.008) = 11.10 mol H atoms [molar mass of H=1.008g/mol]
O: (88.79/16.00) = 5.549 mol O atoms [molar mass of O= 16.00g/mol]
The formula could be articulated as H11.10O5.549.
By dividing the lowest number alter the numbers to whole numbers.
H =11.10/ 5.549 = 2.000
O = 5.549/ 5.549= 1.000
H to O is 2:1
Empirical formula = H2O
A student preformed a chemical reaction and obtained 3.50 grams of the product. According to the balanced chemical equation, the theoretical yield for this reaction is 4.75 grams. What is the percentage yield of the reaction?
The percent yield is calculated by dividing the actual yield (3.50) by the theoretical yield (4.75) and multiplying by 100%.
percentage yield= (actual yield/theoretical yield) x 100%
percentage yield = (3.50 g/4.75 g) x 100%
percentage yield= 74%
Find the molar mass of this compound, if KCl is 10 g:
2KCl3: 2KCl + 3O2
n= m/Mr
10/122.55= 0.08
n= 0.08 mol
*the equation is already balanced, so
m= n x Mr
0.08 x 74.55=
5.97 g
Calculate the amount of solute in moles, present in 2.5 dm3 of a solution whose concentration is 0.2mol/dm3.
The concentration of a solution: 0.2 mol/dm3
The volume of solution:2.5 dm3
Mass of solute= 0.2 x 2.5= 0.5 mol
Calculate the mass of 0.3 moles of Sodium Hydroxide (NaOH). Submit your answer to the nearest whole number.
Molar mass= 22.989769+15.999+1.008=
N= n x L
A sulfide of iron was formed by combining 1.926g of sulfur(S) with 2.233g of iron (Fe). What is the compound’s empirical formula?
Once you find the empirical, find the molecular formula of 414 grams.
Convert grams of each element to moles
Fe: (2.233g /55.85g) = 0.03998 mol =1.008g/mol
S: (1.926 /32.07) = 0.06006 mol S atom =32.07g/mol
Change the numbers to whole numbers.
Fe =0.03998/0.03998 = 1.000
S = 0.06006/0.03998mol = 1.502
We multiply by a number that will give us whole numbers
Fe: (1.000)2 = 2.000
S: (1.502)2 = 3.004
Empirical formula = Fe2S3
Mr= 207.9 g
MF= 414/207.9
MF= 1.99 = 2
2(Fe2S3)
MF= Fe4S6
A student performed a chemical reaction and obtained 2.00 grams of the product. According to the balanced chemical equation, the theoretical yield for this reaction is 3.50 grams. What is the percentage yield of the reaction?
The percentage yield of the reaction is 57.14%.\ Explanation:
The percentage yield is calculated by dividing the actual yield (2.00g) by the theoretical yield (3.50g) and multiplying by 100%:
percentage yield= (actual yield/theoretical yield) x 100%
percentage yield= (2.00g/3.50g) x 100%
percentage yield= 57.14
How many particles are in 8 mol SO2?
N= n x L
N= 8 (6.02 x 1023)
N= 4.816 x 1024g