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Q1) Calculate the molar concentration of 36.5 g HCl in 5 litres of solution Your attempt: mass of HCL 36.5 36.5 5 7.3 M HCL Correct answer: Molar mass HCl 36.5g/mol You have 36.5g HCl, therefore you have 1mol HCl This is dissolved in 5 litres solution Molarity 1/5 0.2M solution Calculate the weight of solute contained in 100 mL of 2 M solution of NaOH Your attempt: ? mol NaOH 0.1 L 2 M NaOH ? mol NaOH 2 x 0.1 answer 0.2 grams or 200mg Correct answer: Molar mass NaOH 40g/mol A 2M solution 2mol per 1000ml or 80g per 1000ml You have only 100 ml, so you have 100/1000*80 8g NaOH in the 100ml solution Calculate the weight of solute needed to prepare a 200mM of NaOH in 100mL Your attempt: ? mol NaOH 0.1 L 0.2 M ? mol NaOH 0.2 x 0.1 = 0.02 grams or 20mg Correct answer: Molar mass NaOH 40g/mol 200millimoles NaOH 200/1000*40 8g NaOH If you dissolve 8g NaOH in 1000ml solution you will have 200mM solution But you want 100ml solution: 100/1000*8 0.8g NaOH requird. Q4) Calculate the weight of NaCl required to prepare a 0.5% solution of NaCl.
many Molar is that? I guess that you want a 5% mass/ volume solution 0.5% 0.5g in 100ml solution. Because you will be calculating molarity, work on 1000ml solution: 5g NaCl in 1000ml solution 0.5% m/v solution Calculate molarity: molar mass NaCl 23+35.5 58.5g/mol 5gNaCl 5/58.5 0.085 mol NaCl.
is dissolved in 1000ml solution Molarity 0.085M Youmust work with the molar mass of the substances you use not the actual mass as you have been doing.
Luck with your studies.
many Molar is that? I guess that you want a 5% mass/ volume solution 0.5% 0.5g in 100ml solution. Because you will be calculating molarity, work on 1000ml solution: 5g NaCl in 1000ml solution 0.5% m/v solution Calculate molarity: molar mass NaCl 23+35.5 58.5g/mol 5gNaCl 5/58.5 0.085 mol NaCl.
is dissolved in 1000ml solution Molarity 0.085M Youmust work with the molar mass of the substances you use not the actual mass as you have been doing.
Luck with your studies.
Sun, 01 Aug 2010 10:19:15 GMT