[astukake]

a) What is the concentration of HCl if it takes 12.0 drops of 1.0M NaOH to nuetralize 8 drops of HCl. The 30 drops of the acid dropper weighed 1.500g and 30 drops of the base dropper weighed 1. 250 grams.

b) Calculate the percent of calcium carbonate in the eggshell from the following data. 0.050 grams of eggshell is dissolved in 25 drops of 2.5 M HCl. After 10 min, it takes 38 drops of 1.0 M NaOH to reach the end point. Assume the drop volume is 0.04ml. The molar mass of CaCO3 is 10 g/mol.

c) Picture the interactions between Na OH and H20. Be able to draw picutres. I tried them all. But especially c, I am struggling. Please be specific about c. about the type of bonds and stuff. Thank you so much.

[Unknown008]

a) There must be an assumption you have to make here that you didn't mention, or some other given information. This is impossible to solve unless you have the relation between the volume of a drop and its mass.

Otherwise, if you know the volume, find the volume of 12 drops of NaOH and hence, find the number of moles of NaOH used for the neutralisation reaction. Then write down the balanced equation for the reaction and find the number of moles of HCl present in the 8 drops of acid. From there, find the volume of the 8 drops of acid and with the number of moles and the volume, find the concentration of the acid.

b) Same thing here. When you get the number of moles of acid reacted with the base, find the number of moles of acid initially present in the 25 drops of 2.5M HCl. Find the difference and write down the equation for the reaction between HCl and CaCO3. From that equation, you can find the mass of Ca in the eggshell and find the percentage of Ca by mass in the eggshell.

PS. The molar mass of CaCO3 is not 10, as Ca itself is 40 g/mol ;)

c) NaOH is first a solid. What would happen when it dissolves? You get Na^+ and OH^- ions. Now, what is the nature of water? Water is a polar molecule (that is there is one slightly more positive part than the other part) and hence, these will surround each of the ions. Can you picture which part will be towards the Na^+ ions and which parts will be towards the OH^- ions?