Chemistry help!!!? urgent!!?

I need some help on these questions

9x10^4L of rainwater with an average hydrogen ion concentration of 1x10^-4g/L was collected and stored in a galvanised iron tank. After several months the pH of the water was found to be 7. Assuming the zinc was the only material in contact with the water, calculate the

a) mass of zinc that would of dissolved

b) the concentration of zinc ion, in mol/L, in the rainwater

Sweat is a solution containing mainly sodium,potassium, chloride ions. The concentration of hydrogen ions in sweat= 1x10^-5g/L. Calculate the mass of solid calcium hydroxide required to neutralise 10mL of sweat

a) Calculate the concentration in mol/L, of a sodium carbonate solution produced from 250g sodium carbonate 10 water dissolved into 2L of water to produce 2.1L of solution

b) If sodium carbonate neutralized hydrochloric acid, calculate the mass of sodium chloride produced if all of the 2.1L sodium carbonate solution reacted with the acid

To determine the purity of limestone, mostly calcium carbonate, an analyst measured the mass of a small sample of limestone to be 2.59g. He placed enough HCl into a beaker to completely dissolve the limestone sample. The beaker and acid had a mass of 110.61g. He then placed the limestone sample into the acid and allowed it to completely dissolve. After the reaction was completed the mass of the beaker and it s contents was found to be 112.22g. Calculate the percentage purity of the limestone.

Any help is great, thx