Flame tests to identify some metal cations and metals.


Flame tests are a simple and effective way to identify the presence of certain metal cations in a sample. The principle behind flame tests is that when a metal cation is heated in a flame, it will emit light of a specific color that can be used to identify the metal cation.

Experimental Method:

  1. Obtain a Bunsen burner and a clean wire loop.
  2. Prepare a solution of the metal cations to be tested.
  3. Dip the wire loop into the solution and hold it in the flame.
  4. Observe the color of the flame and compare it to a known color chart or reference.
  5. Repeat the test for different metal cations to identify them.

Data Analysis:

The color of the flame can be used to identify the metal cation present in the sample. Different metal cations will emit different colored flames. For example, sodium ions produce a yellow flame, copper ions produce a blue-green flame, and lithium ions produce a red flame.

Conclusion:

Flame tests are a simple and effective way to identify the presence of certain metal cations in a sample. By observing the color of the flame, it is possible to identify the metal cation present in the sample. It’s important to note that flame tests can give false positives, so chemical tests like spectroscopy should be used to confirm the results.

Position vs. Time and velocity vs. time for a free-falling object:


The position of a free-falling object is measured downward from a certain starting point.

The position of the object increases with time as it falls.

The graph would be a straight line with a negative slope, starting at the initial position and ending at the final position.

Velocity vs. Time graph for a free-falling object:

The velocity of a free-falling object increases with time as it falls.

The graph would be a straight line with a positive slope, starting at zero and ending at the final velocity.

To determine the acceleration due to gravity, we can use the equation:

a = v^2/s or a = 2s/t^2

Where a is the acceleration, v is the final velocity, s is the final position, and t is the time of fall.

Since the acceleration due to gravity is constant, the slope of the velocity vs time graph is the acceleration.

Position vs. Time:

The graph for position vs. time for a free-falling object would be a straight line that starts at a non-zero position (the initial height of the object) and decreases as time goes on. The slope of this line would represent the velocity of the object. The equation for this line would be:

y = -g*t + h

where g is the acceleration due to gravity, t is the time, and h is the initial height of the object.

Velocity vs. Time:

The graph for velocity vs. time for a free-falling object would be a straight line that starts at a non-zero velocity (the initial velocity of the object) and decreases as time goes on. The slope of this line would represent the acceleration of the object. The equation for this line would be:

y = -g*t + v

where g is the acceleration due to gravity, t is the time, and v is the initial velocity of the object.

Determining the Acceleration due to Gravity:

To determine the acceleration due to gravity, we can use the slope of either the position vs. time or velocity vs. time graph. For the position vs. time graph, the slope is -g, and for the velocity vs. time graph, the slope is -g. Therefore, we can conclude that the acceleration due to gravity is -g.

GRADE 12 PRESCRIBED EXPERIMENT 2: ACID-BASE REACTIONS 


                                 

WORK SHEET 
TOTAL MARK: 50

ACTIVITY

Titration of oxalic acid against sodium hydroxide to determine the concentration of the sodium hydroxide.

In this investigation you will prepare an acidic solution accurately and thus you will know its exact concentration. You will then react this acid with a base of an unknown concentration to determine the concentration of the base.

What you will need:

Erlenmeyer flasks,
Burettes,
Burette clamp,
Medicine  dropper,
Retort stand,
White tile /paper,
Measuring cylinders,
Mass meter
Oxalic acid,
Sodium Hydroxide,
Phenolphthalein as indicator,
Funnel,
Beaker,
Spatula,
Glass rod,
Pipette with sucker

What to do:

  1. Prepare a standard solution of oxalic acid which has a concentration of approximately 1mol.dm-3.
  2. Now prepare a sodium hydroxide solution by dissolving approximately 2g of dry sodium hydroxide in 500ml of water.
  3. Add two drops of the indicator solution.
  4. Place the burette in the clamp.
  5. Using the funnel, fill the burette to above zero mark with the acid solution.
  6. Then, holding the beaker, with which you used to pour the acid, beneath the burette, gradually open the tap.
  7. Allow the level of the base to come down to exactly zero (reading from the bottom of the meniscus).
  8. Pipette using the sucker exactly 25ml of oxalic acid solution in a volumetric flask.
  9. Add a few drops of phenolphthalein to the acid.
  10. Hold the conical flask beneath the burette with your right hand and gradually open the tap with your left.
  11. Swirl the conical flak continuously and watch it closely for the first sign of a colour change.
  12. As you see that you are approaching the point of neutralization, close the tap slightly so that you are adding drop by drop.
  13. When the colour changes completely the titration is finished.
  14. Close the tap and read from the burette how much acid was used.
  15. Repeat this procedure at least twice so that you have three readings for the volume of NaOH (of unknown concentration) required to neutralize exactly 25ml of oxalic acid (of known concentration).
  16. Take an average of these three and use it to calculate the concentration of the NaOH.
  17. Now calculate the concentration of the sodium hydroxide solution.
  18. Make a neat labeled sketch to represent the apparatus
  19. Now write a report using the format learnt in class.

     Questions

  1. What is the appropriate concentration of NAOH (2g in 500ml of water)
  2. Calculate the theoretical concentration of NaOH from the actual mass of NaOH you measured.
  3. How does your theoretical value for NaOH concentration (from the actual mass you measured) differ from the actual concentration you calculated (from the titration procedure)? Can you think of some reasons why your values may differ?

Chemical equilibrium


INTERMOLECULAR FORCES