i have some chemistry math questions and i have no idea how to do them! =[?

Question

1.When the dyes present in green ink are seperated by paper chromatography, the distance traveld by the water is 10cm, the distance traveld by the yellow dye is 8cm, and the distance traveld by the blue dye is 5cm. Calculate the retention factor for the blue dye.

2.Is the mass of one dozen cookies of uniform size, shape, and mass is 156 grams, calculate the mass of a single cookie.

3.calculate the volume of a marble which when place in a graduated cylinder containing 60.0 milliliters of water, raised the volume of the water to 67.0 milliliters

4.If a solid copper cube is placed in a graduated cylinder and it displaced 27.0 milliliters of water, what would be the enge lenght of the cube?

5.If a cube has an edge lenght of 2.00 centimeters and its mass is 5.00 grams, calculate its density.

6.ice has a density of 0.92 g/cm^3. what is the volume of 1.8 kilograms of ice?

Answer 1

1. Retention factor is usually called the Rf value. It's distance traveled by the solute divided by distance traveled by the solvent. The solute is the blue dye. The solvent is the water. So 5cm/10cm is 0.5. Notice that this is a unit-less value. The length measures of the numerator and denominator cancel.

2. If all twelve identical cookies weighed 156 grams in the bag then one of those cookies weighs one twelfth of 156 grams. 156/12 = 13 grams

3. When you put the marble in it displaces some water, takes up some additional room. That volume is the difference between the final measure and the initial measure. 67.0 mL - 60.0 mL = 7.0 mL. Since the marble is solid we usually express the volume in cm^3. 1 cm^3 = 1 mL, so they are equivalent. So the answer is 7.0 cm^3.

4. Since it displaced 27.0 mL the volume of the cube is 27.0 mL which we'll find it easier to write as 27.0 cm^3. Since we're dealing with a cube we know that the equation for its volume is

length^3 = volume

Let x stand for the length. Just fill in the quantity we know and solve:

x^3 = 27.0

So ask yourself the question. What cubed is equal to 27? The answer is 3. 3 X 3 X 3 = 27.

So the answer is 3.00 cm

5. Again we have a cube so the volume is easy to calculate. (2.00cm)^3 = volume
Volume = 8.00 cm^3
Density equals mass divided by volume. So 5.00/8.00 = 0.625g/cm^3

6. Do this with conversion factors:

1.8 kilograms * (1000 grams/1 kilogram) = 1800 grams
1800 grams * (cm^3/0.92 g) = 1956 cm^3

Remember you only have two significant figures so 9 is the last significant figure and should be rounded. This gives you a figure of 2000 cm^3. Since we only have 2 sig figures, and this figure implies 4 sig figures, we should express in scientific notation as 2.0 * 10^3 cm^3

Answer 2

I think the problem is that the questions are set in a very confusing way. I don't know why schools do this.

1) Rf just means distance travelled by the substance (in your case the blue dye) divided by distance travelled by the solvent (in your case the water). That's all!

2) If a dozen cookies cost 156 cents, how much as one cookie cost?

If a dozen cookies weigh 156 g, how much does one cookie weigh?

3) if you drop something into water and it sinks, and the water is in a graduated cylinder, the total volume measured is just the volume of the water + the volume of what you put in it.

4) your cube displaces 27 ml of water. 1 ml = 1 cubic centimetre. You can probably see the answer now; if the edge of the tube was 2 cm, it would displace 8 ml water.

5) density = mass divided by volume. So find the volume of the cube and divide the mass by it.

6) again, density = mass divided by volume. This time, it is the volume that you want, so you need to make it the subject of the equation:

Volume = mass divided by density

Find the mass in g, use the density you are given, an out will come the answer in cm^3.

Why the question uses cm^3 in (6), but ml in (4), I have no idea. If your teacher is sympathetic, explain to him or her that you find this confusing, if you do. I would have when I was just starting.

Answer 3

1.?????
2. 156/12= mass of 1 cookie
3. 67-60=7ml H2O displaced, 1ml=1cm^3
volume = 7cm^3
4. 27.0 ml=27.0 cm^3 take the 3rd root to find the length of one side= 3cm
5. 2.00^3=8 cm^3; density =g/cm^3 so
5.00 g / 8cm^3= the density of a cube
6. 1.8 kg * 1000= 1800 g
1800g * (1 cm^3 / 0.92 g) = the volume of the ice