Choose the correct one:
1) 25.00 mL is taken from a solution containing NaOH, NaHCO3 and Na2CO3 individually or as a mixture.
up to the phenolphthalein milestone when analyzed
When 11.00 mL of 0.100 M HCl is taken and a second 25.00 mL is taken and titrated to the bromocresol green turning point, 11.02 mL of HCl is consumed. Find the composition of the solution.
a) NaOH
b) NaHCO3
c) Na2CO3
d) NaOH+ Na2CO3
e) NaHCO3 +Na2CO3
2) H2C2O4 with concentrations of 0.0400 M and 0.200 M
Calculate the pH of a solution containing NaHC2O4.
(Ka1 = 5.60x10-2; Ka2 = 5.42x10-5)
a. 1.01
b. 3.45
c. 4.08
D. 5.67
E. 6.89
3) Containing cadmium (Cd2+) and lead (Pb2+) ions
The titration of a 25.00 mL sample with 0.0040 M EDTA consumes 39.10 mL of EDTA. The cadmium in the sample is then masked by forming Cd(CN)4^-2 with excess KCN. This time 28.00 mL for titration
EDTA is wasted. Cd2+ (112.4 g mol-1) in the sample and
Pb2+ (207.2 g mol-1) concentrations are given below
which one?
Pb2+ (M) / Cd2+ (M)
a. 0.112 /0.044
b. 1.1×10-2 / 4.4×10-3
c. 4.48×10-2/8.8×10-3
D. 4.48×10-3/8.8×10-4
E. 8.8×10-3/4.48×10
To solve these questions, we need to use some concepts from chemistry. Let's break down each question and explain how to find the correct answer.
1) In this question, we have a solution containing NaOH, NaHCO3, and Na2CO3. We are titrating it with HCl and observing the volume of HCl consumed. We are given two different volumes of HCl consumed for two different titrations. The first titration is up to the phenolphthalein milestone, and the second titration is up to the bromocresol green turning point.
To find the composition of the solution, we need to analyze the change in volume of HCl consumed during the two titrations. The volume difference will give us information about the presence or absence of the three compounds.
Step 1: Calculate the moles of HCl used in the second titration.
Moles of HCl = Concentration of HCl × Volume of HCl used (in L)
Moles of HCl = 0.100 M × 0.01102 L
Step 2: Calculate the moles of HCl used in the first titration.
Moles of HCl = Concentration of HCl × Volume of HCl used (in L)
Moles of HCl = 0.100 M × (0.02500 L - 0.01102 L)
Step 3: Determine the moles of each compound based on the difference in moles of HCl used in the two titrations.
The difference in moles of HCl consumed will correspond to the moles of Na2CO3, while the difference in volume of HCl used will correspond to the moles of NaHCO3.
If the difference in moles of HCl consumed is zero, it means Na2CO3 is absent.
If the difference in volume of HCl used is zero, it means NaHCO3 is absent.
Based on the analysis, we can determine the composition of the solution.
2) In this question, we are given the concentrations of H2C2O4 (oxalic acid) and asked to calculate the pH of a solution containing NaHC2O4 (sodium hydrogenoxalate).
To calculate the pH, we need to consider the dissociation of both Ka1 and Ka2 of oxalic acid in water. We can use the equations for the dissociation constants and the expression for pH to arrive at the answer.
Step 1: Write down the dissociation equations for oxalic acid (H2C2O4).
H2C2O4 ⇌ H+ + HC2O4-
HC2O4- ⇌ H+ + C2O4-2
Step 2: Write down the equilibrium expressions for Ka1 and Ka2.
Ka1 = [H+][HC2O4-] / [H2C2O4]
Ka2 = [H+][C2O4-2] / [HC2O4-]
Step 3: Set up an equation for pH using the given concentrations and dissociation equations.
[H+] = √(Ka1 × [H2C2O4] / [HC2O4-]) + √(Ka2 × [HC2O4-] / [C2O4-2])
Step 4: Calculate the pH using the equation derived in Step 3.
3) In this question, we have a solution containing Cd2+ and Pb2+ ions. We are titrating it with EDTA (ethylenediaminetetraacetic acid), and the volumes of EDTA used for titration are given for two different cases.
To find the concentration ratio of Pb2+ to Cd2+, we need to consider their reaction with EDTA and the stoichiometry of the reaction. The reaction between Pb2+ and Cd2+ with EDTA forms stable complexes, and the volume of EDTA used for each case corresponds to their molar ratios.
Step 1: Determine the moles of EDTA used in each case.
Moles of EDTA = Concentration of EDTA × Volume of EDTA used (in L)
Step 2: From the balanced reaction equation, determine the stoichiometric relationship between EDTA and the metal ions (Pb2+ and Cd2+).
Step 3: Use the moles of EDTA and the stoichiometric relationship to calculate the moles of Pb2+ and Cd2+ in each case.
Step 4: Using the moles of Pb2+ and Cd2+ obtained from Step 3, calculate their concentrations in each case.
Step 5: Compare the concentrations of Pb2+ to Cd2+ and choose the correct option based on the given concentrations.
By following these steps, you can find the correct answer for each question.