Exam Review #20

20) Use stoichiometry to solve the following complex problems:

A.   If a sample of K₂S is known to contain 8.418x10²⁴ atoms of K, what mass of potassium sulfide is present?

8.418x10²⁴ atoms K x          1 mol K           x  1 mol K₂S x 110 mol K₂S =  769 mol K₂S

                                    6.022x10²³ atoms K     2 mol K       1 mole K₂S

B. How many chloride atoms can be found in 38.0L of CCl₄ gas at STP?

38.0 L CCl₄ x 1 mol CCL₄ x   4 mol Cl x 6.022x10²³ atoms Cl = 4.10 atoms CL

                       22.4 L CCl₄   1 mol CCL₄  1 mol Cl

C. If a sample of carbon monoxide gas has a volume of 20.8L at STP, how many grams of oxygen are present?

20.8L CO x 1 mol CO x 1 mol O  x 16.0g O = 14.9g O

                     22.4L CO    1 mol C     1 mol O

Exam Review #16

How did Thomson determine that the cathode ray was negatively charged?

In the late 1800s, experiments were performed where electic currents were passed through various gases at low pressures. It was noticed that when current was passed through a cathode-ray tube, the surface directly opposite of the cathode in the tube glowed. They hypothesized that the glow was caused by a stream of particles, called cathode ray. The ray went from the cathode (a metal disk) to the anode (a metal disk).

In the Cathode Ray Tube Expirament JJ Thomson put a postitive and a negative magnet on opposite sides of the Cathode Ray, instead of going straight, the particles were deflected by the negative magnet. It was observed that:

1. Cathode rays were deflected by a magnetic field in the same manner as a wire carrying electic current, which was known to have a negative charge.

2. The rays were deflected away from a negatively charged objects.

These observations led to the hypothesis that the paricles that make cathode rays are negatively charged. J J Thomson had an investigation where he was able to measure the ratio of the charge of cathode-ray particles to their mass. The ratio was always the same, no matter what metal he used to make the cathode or the nature of the gas inside the cathode-ray tube. He concluded that all cathode rays are made up of indentical negatively charged paricles, which were named electrons.

Physical Properties of Vinegar

• The color of Vinegar is clear, but when mixed with a food dye, it changes the color of the food dye. The color of vinegar is a physical property because it does not change the identity of the substance in order to be observed.
• apple-cider-vinegar-benefits.com says that the freezing point of vinegar is -2ºC. Freezing point is a physical property of vinegar. Like color, the freezing point does not change the identity of the substance in order to be measured.
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• apple-cider-vinegar-benefits.com says the boiling point of vinegar is 100.6ºC. Along with the boiling point property, there was also steam coming from the boiling vinegar, which is another physical property. Boiling vinegar shows the physical change of a substance from one state to another.
• apple-cider-vinegar-benefits.com says that the density of vinegar is 1.01 g/mL. Density is an intensive physical property, because it is the same no matter how much of it you have.
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• The volume of vinegar I used was 100 mL. Volume is an extensive physical property, because it relies on how much vinegar you have.

Chemical Properties in VInegar

• Vinegar reacts with egg white to create precipitates
• Vinegar reacts with Drano generating energy exothermically
• Vinegar reacts with baking soda, by creating a frothy white foam, which overflowed the bowl.
• Vinegar reacted with milk by forming precipitates

• Vinegar rusts steel wool

At Home Expirament

For my at home expirament, I chose vinegar as my object to record five chemical, and five physical properties.

sources used: http://www.apple-cider-vinegar-benefits.com/