Chemistry-Density questions?

Question

1. An object weighs 45g its denisty is 12.9g/cm. When measured its height is 7.43 cm and width is 3.45. How long is the object?

2. Solid sodium chloride has a denisty of 2.16g/cm/ A chemist needs 56.1 mL of sodium chloride. How many grams should the chemist use?

Answer 1

1.
m = mass
d = density
h = height
w = width
l = length
v = volume
* = multiply

d = m/v by definition
so v = m/d

v = l*w*h

therefore

v = m/d = l*w*h
and l = m/(d*w*h)

just plug in the numbers. And make sure to convert to proper units so the units cancel out.

2. d = m/v
so m = d*v

thats it.

Answer 2

1. The object reads 45g on a scale, its mass -= 45gm by convention. mass = volume x density, or

volume = mass / density.

You didn't say what shape the object is. Is it a cylinder? In any case, the volume of the object is base area times length (assuming it's straight-sided, something else not given). Find the volume from the mass/density. Find the length from L=V/A, where V = volume just calculated, and A = area of the base.

2. Using the equation mass = density x volume, you have the density and the volume; you can figure the mass.

Answer 3

1. Density(D) = mass(M)/volume(V)

Re-arrange the equation and you find that V=M/D. From that, figure out what the volume is.

Now, set V = Height * Width * Length. You have H and W, solve for L.

2. Use D=M/V. From this you know that M = D/V. You have the density and the volume, so solve for M. Don't foget that 56.1 mL is the same as 56.1 cm^3.