Molar Concentrations
How would you make 500 mL of a 0.05 M NaCl solution?
MW of NaCl: 58.44 g/mol
You weigh 1.461 g of NaCl and add diluent up to the 500 mL mark.
Solution:
1M NaCl = 1 mol/L = 58.44 g/L
58.44 g/L x 0.5 L = 29.22 g
29.22 g x 0.05 = 1.461 g
How much NaCl would you need to weigh out to create 1L of 0.9% NaCl solution?
Assuming density is 1 g/ml
What is 9g of NaCl.
Mass of NaCl=(Percentage concentration/100) ×Volume of solution×Density of solution
mass = 0.009 x 1000 x 1
mass = 9
Prepare 50 mL of a 3% solution from a 4% solution. 🧍
50/4 = 12.5 mL x 3 = 37.5 mL
What is taking 37.5 mL of the 4% solution and add diluent up to the 50 mL mark ⛹️
How would you prepare 1 ml of a 1:5 dilution of sera?
D1 = 1, D2 = 5, V1 = X, V2 = 1
D1/D2 = V1/V2
1 / 5 = X / 1
X = 0.2 ml
Thus, 0.2 ml (undiluted serum) + 0.8 ml of saline = 1.0
If 0.1 mL of a urine culture from a 10-6 dilution yielded 38 colonies, how many bacteria were there per ml in the original sample?
(38 * 106 )/0.1 mL = 3.8 * 108 CFU/mL
How much arginine do you need to make a 0.01M solution of arg?
MW of Arg: 174.20 g/mol
You weight 1.742 g of arg and add diluent up to the 1 L mark.
Solution:
174.20 g/mol x 0.01 mol/L = 1.742 g
If a 500ml solution was reported to have a 15% concentration of X substance, how much X in g is in the solution?
Assume density is 1g/ml
What is 75g.
Mass of X=(Percentage concentration/100) ×Volume of solution×Density of solution
mass= 0.15 x 500 x 1
mass = 75
Prepare 100 mL of 10% alcohol from 95% alcohol. 🙀
(100 mL) (10%) = (x mL) (95%)
x = 10.5 mL
What is taking 10.5 mL of the 95% alcohol solution and adding diluent up to the 100 mL mark 😾
How would you prepare 8 mL of a 1:20 dilution of sera?
D1 = 1, D2 = 20, V1 = X, V2 = 8
D1/D2 = V1/V2
1 / 20 = X / 8
X = 0.4 ml
Thus, 0.4 ml (undiluted serum) + 7.6 ml of saline = 1:20
How many bacteria were present in the following sample?
Dilution: 10-7
Volume Plated: 0.1 mL
Number of Colonies Counted: 26
(26 * 107)/0.1 mL = 2.6 * 109 CFU/mL
How much arginine do you need to make 100 mL of a 0.01 M solution of arg?
MW of Arg: 174.20 g/mol
You weigh 0.1742 g of arg and add diluent up to the 100 mL mark.
Solution:
174.20 g/mol x 0.01 mol/L x 0.100 L = 0.1742 g
If a solution was created using 50g of substance X and filling the remaining 750 ml beaker with DI water, what is the concentration of substance X in this solution?
assume density 1g/ml
What is approximately 6.67?
Concentration = (mass of X/ Total volume) x 100
concentration = (50/750) x 100
concentration = 6.67
Volume of a 0.02% solution that can be prepared from 25 mL of a 0.1% solution 🤫
(25 mL) (0.1%) = (x mL) ( 0.02%)
x = 125 mL
What is 125 mL 🐐
You have a stock solution of protein containing 10 grams per ml. You want a concentration of 2 mg/ml. How would you perform this dilution in just three steps?
IC/FC = 10,000 / 2 = 5,000
Dilution Factor= 5,000
Step 1 – 1 ml of 10,000 mg/ml stock solution + 49 ml of diluent = 1:50 dilution = 200 mg/ml
Step 2 – 1 ml of 200 mg/ml + 9 ml of diluent = 1:10 dilution = 20 mg/ml
Step 3 – 1 ml of 20 mg/ml + 9 ml of diluent = 1:10 dilution = 2 mg/ml
How many bacteria were present in the original sample?
Dilution Volume Plated # of Colonies
10-2 0.1 mL 241
10-3 0.1 mL 35
10-4 0.1 mL 7
10-5 0.1 mL 0
What is 2.95 x 105 CFU/mL
What is the molarity of a solution that was prepared by dissolving 14.2 g of NaNO3 in enough water to make 350 mL of solution?
MW of NaNO3: 85 g/mol
0.477 M
Solution:
14.2 g x 1 mol/85 g x 1/0.35L = 0.477 M
If a 1000ml solution was created using 50g of substance X, 70g of substance Y, and filled the remainder of the beaker with DI water, what are the concentrations of the two substances in the solution?
assuming density 1g/ml
What is 5% of X and 7% of Y.
Concentration of X: Concentration of X (%)=(50g/1000 ml)×100
Simplify the calculation: Concentration of X (%)=5%
Concentration of Y: Concentration of Y (%)=(70g/1000 ml)×100
Simplify the calculation: Concentration of Y (%)=7%
Percent concentration of alcohol prepared when 10 mL of 95% alcohol are diluted with H2O to make a final volume of 38 mL 🦧
(10 mL) (95%) = (38 mL)(x%)
x = 25%
What is 25% concentration of alcohol 🦍
You have a stock solution of 10 g/ml of vitamins and want to obtain a solution of 0.5 mg/ml. How would you perform this dilution in just three steps?
IF/FC = 10,000 / 0.5 = 20,000
dilution factor = 20,000.
To perform a 1:20,000 dilution,
Step 1 – 1 ml of 10,000 mg/ml +19 ml of diluent = 1:20 dilution = 500 mg/ml
Step 2 – 1 ml of 500 mg/ml + 99 ml of diluent = 1:100 dilution = 5 mg/ml
Step 3 – 1 ml of 5 mg/ml + 9 ml of diluent = 1:10 dilution = 0.5 mg/ml
Image Based Question 2 (18)
What is 2.01 x 106 CFU/mL
How many grams of NaBr would be needed to prepare 700 ml of 0.230 M NaBr solution?
MW of NaBr: 102.9 g/mol
16.6 g NaBr
Solution:
0.230 mol/L x 0.700 L x 102.9 g/mol = 16.6 g
Someone with short-term remembery loss created a solution using 18g of substance X and forgot how much DI water they put in but remembered that the concentration of X was 20%. What was the total volume of the initial solution?
Assume density is 1g/ml
What is 90ml
concentration = (mass of x/total volume) x density
20% = (18/total volume) x 1
0.2 = 18/total
total = 90
Percentage of dextrose that is prepared when 3 mL of a 10% dextrose solution are mixed with 12 mL of broth 😟
(3 mL) (10%) = (12 mL) (x%)
x = 2%
What is 2% dextrose solution 😍
You want a 1:3,000 dilution of serum and you need 2 ml. How would you perform this dilution in several steps?
3000 / 2 = 1,500
Step 1 – 1 ml of serum + 29 ml of diluent = 1:30 (individual dilution)
Step 2 – 1 ml of 1:30 dilution + 9 ml = 1:10 (individual dilution)
Step 3 – 1 ml of 1:10 dilution + 9 ml = 1:10 (individual dilution)
Image Based Question 3 (23)
What is 8.4 x 1010 CFU/mL