8.2 pH: A Measurement Scale for Acids ano 8.2 Calculating pH from Acid Molarity

Question

8.2 pH: A Measurement Scale for Acids ano 8.2 Calculating pH from Acid Molarity EXAMPLE LEARNING GOAL 4 Calculate pH from Calculate the pHof a 1.0 x 10 3M solution of Hcl. Solution Step 1. Recognize that HCl is a strong acid; consequently, it is 100% dissociated. Step 2. One Hao is produced for each HCI. Therefore a 1.0 x 10 3 MHCI solution has lHto 1-1 Step 3. Using our expression for pH: pH -log [H so l Step 4. Substituting for [H3O pH log 11.0 x 10 31 l 3.001 3.00 Practice Problem 8.2 Calculate the pH of a 1.0 x 10 M solution of HNO For Further Practice: Questions 8.49 and 8.50 our The proper use of the logarithm function often ears to contradict and of significant figures. This is because appe is an exponent the hn information in the measurement

Explanation / Answer

Problem 8.8

a)

calculate concentration of NaOH if

V = 40 mL of solution required for

V = 20 mL of M = 0.2 M of HCl

so

ratio is 1:1 HCl:NaOH

so

mol of HCL = MV = 20*0.2 =4 mmol

so

mmol of NaOH = 4

M = mmol/mL = 4/20 = 0.2 M for NaOH

b)

Same case

M1 = ?

V1 = 36 mL

M2 = 0.2 M

V2 = 25 mL

so

mmol of acid = mmol of base

M1*V1 = V2*M2

M1 = M1*V1/V2 = 0.2*25/36

M = 0.1388888 of NaOH

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