Lab Math

Question 1

What formula would you use to look for the pH of a substance given its hydrogen ion concentration?

Answer 1

pH = - log [H⁺]

Question 2

Prepare 100g of 5% aqueous soulution of hypochloric acid (Using 12M HCl).

Answer 2

Formula of Weight / Weight: % Solution = grams solute / grams of solution

5% = 0.005

0.005 = x grams / 100 grams water

x = 5 grams of HCl

Question 3

Given 1L of a 10% (w/v) solution of NaOH, calculate the amount of NaOH (in grams) needed to produce this solution.

Answer 3

Formula of Weight / Volume: % solution = Weight in grams of Solute / Volume of Solution in mL (units very depending on the requirement of the question)

10% = 0.10

0.10 = x grams of NaOH / 1000mL of Solution

x = 100 g of NaOH

Question 4

Make up 50 mL of a 2% (v/v) concentrated HCl soln.

Answer 4

Formula of Volume / Volume: % Solution = Volume of Solute / Volume of Solution

2% = 0.02

0.02 = x Volume of solute / 50 mL of Soln

x = 1

Question 5

Molarity is expressed in what two common units?

Answer 5

M is expressed in moles per liter and millimoles per milliliter.

Question 6

Find the incorrect pair:

1. 1 mol = gmw of substance
2. M = mol / mL
3. W / W = g of solute / g of solution
4. W / V = g of solute / mL of solution
5. All pairs are correct
6. > 1 pairs are incorrect

Answer 6

2. M = mol / mL

M = mol / L or mmol / mL

Question 7

What is the N of a 500-mL solution that contains 7g of Sulfuric Acid?

Answer 7

Formula for Normality: No. of eq of solute / L of solution

eq of H2SO4: 1 eq / 49 g (gmw of H2SO4 is 98 / 2 (valence) )

N = 7g / 500 mL * 1 eq / 49 g H2SO4 * 1000 mL / 1 L

N = 0.285

Question 8

What is the formula that directly relates Molarity and Normality?

Answer 8

Normallity = Molarity * Valence

Question 9

Convert 8.2 mg / dL of Ca to mmol / L

Answer 9

Formula for conversion: mg / dL * dL / mL * 1000 mL / L * mmol / mg

8.2 mg / dL * 1 dL / 100 mL * 1000 mL / 1 L * 1 mmol / 40g (gmw of Ca is 40 g per mol, same for mmol)

Question 10

How do you calculate the concentration of a diluted substance given its initial concentration and both initial and final volume?

Answer 10

C1V1 = C2V2

Question 11

What is expressed in dilution?

Answer 11

volume of solute / volume of solution

i.e. 1:10 NaOH and 1 / 10 NaOH means 1 mL of NaOH is to 10 mL of NaOH + H2O solution

Question 12

When do you use the dilution factor?

Answer 12

When moving from a lower concentration to a higher concentration.

Question 13

Give the formula for Beer’s Law

Answer 13

Concentration of std. / Absorbance of std. = Concentration of unknown / abosrbance of unknown

Question 14

Celsius to Fahrenheit

Answer 14

F = 9/5 * C + 32

Question 15

Fahrenheit to Celsius

Answer 15

C = 5/9 * (F - 32)