Calculate the amount of water (in grams) that must be added to each of the following substances to produce the indicated solution. (a) 1.90 g of urea (NH2)2CO in the preparation of a 20.6 percent by mass solution: g (b) 31.1 g of MgCl2 in the preparation of a 7.2 percent mass solution: g

Select all of the statements which are true. electrons are located in shells or orbits around the atom. electrons orbit slowly around the atom. electrons travel in one flat path around the nucleus of an atom. the valence of an atom is determined by the number of electrons in the atom's outermost shell.

If 15 drops of ethanol from a medical dropper weight 0.60g, how many drops does it takes from a dropper to dispense 1.0ml of ethanol? the density of ethanol is 0.80g/ml

The rate constant for the reaction below is 6.2 x 10−5 mol l−1 s −1. if the initial concentration of a is 0.0500 m, what is its concentration after 115 s?