What mass of K3PO4 is required to prepare 400mL solution that contains 6 x 10^21 K3PO4 particles per liter of solution?  ( atomic masses are  K=39amu, P=31amu  O=16amu)

Household ammonia contains 0.85 g of NH3 in each 100. mL ofsolution.
What is the molarity of the ammonia solution?
(atomic masses: N = 14.01, H = 1.008)

what is the pH of an aqueous solution that contains 5.3 x 10-7 OH ions per liter of solution?

What mass of (NH4)2Fe(SO4)2*2 H2O (Solid) is required to preparea 500mL solution containing 100 ppm in Fe? 2. Using this stocksolution, what aliquot must be used to prepare calibrationsolutions, 100-mL volumes, of the following: (a) 0.100 ppm, (b)0.500 ppm, (c) 2.00 ppm, (d) 4.00 ppm and (e) 7.0 ppm.