The mass of an atom may be determined by adding the masses of the protons and neutrons in the nucleus. Why is it unnecessary to include the electrons when determining the mass of an atom?

The frequency of a given region of the electromagnetic spectrum is more than 3 x 1019 HZ. Note that the speed of light is 2.998 x 108 m/s. Which waves are found in this region? A. gamma rays B. visible light C. microwaves D. radio waves E. x-rays

A 425-ml sample of hydrogen is collected above water at 35°c and 763 torr. find the volume of the hydrogen sample when the temperature falls to 23°c, assuming the barometric pressure does not change. (vapor pressures of water : at 35°c, 42.

If methyl orange is added to a substance and it turns the substance red, what does this tell you about the pH of the substance? Would this substance be an acid or a base?

What is any condition in an experiment that can be changed

MnO2 + 4 HCl → Cl2 + MnCl2 + 2 H2O Given 145.7 grams of MnO2, how much hydrochloric acid (HCl) is needed to use up the MnO2 completely (MM in g/mol: MnO2=86.94, HCl = 36.46, Cl2=70.9, MnCl2=125.84, H2O=18.02) ? 244.4 g 10.55 g 145.5 g 1407 g

Hydrochloric acid is purchased in 12 molar concentrations. If I needed 200 ml of 2.0 molar HCl, how many milliliters of the concentrated solution would I need

Which of the following represents a chemical change? Bending a wire Freezing of water Fireworks exploding Melting of a wax candle

5.00 L of a gas is collected at 100K and then allowed to expand to 20.0 L. What must the new temperature be in order to maintain the same pressure? A. 400 °C B. 127 °C C. 223 °C D. 627°C

Before the initial explosion was the matter hot or cold

Which of the following atoms has seven valence electrons? chlorine (Cl) nitrogen (N) manganese (Mn) oxygen (O)