Interesting Chemical Reactions

  1. Cabbage indicator

Red cabbage juice is a natural pH indicator and is one of the most popular chemistry experiments for children. The indicator changes from purple to bright pink in acids (e.g. lemon juice or vinegar)  to blue or yellow-green in bases (detergent, soap).  Students can use this pH indicator to classify a variety of safe household chemicals including vinegar, laundry powder and lemonade.

Acids and alkalis

Acids have a sour taste, like vinegar (which contains ethanoic acid) and lemons (which contain citric acid).

Alkalis are substances bitter and soapy substances that react with acids and neutralise them. Soap and washing powder are alkaline.

Acids and alkalis are found in a surprising number of places. Some are edible and are found in foods. Others are very strong and can be harmful, such as the acid in car batteries and the alkali in oven cleaners.

 

Acids and bases – this experiment uses acids and bases
Natural chemicals – this experiment can be used to introduce the concept that chemicals found in nature can be of use to humans (i.e. as pH indicators). Reactions of acidic and basic substances with an indicator involved colour changes. This experiment can be used to illustrate chemical reactions, which would usually involve colour changes.

Lesson plan 

 

Powerpower point:  red_cabbage_indicator

 

Videos:

 

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Kinematics – Motion in a plane

 

1. A coordinate system provides a systematic means of specifying the position of a particle. A system in one dimension involves choosing an origin and a positive direction in which values of the position coordinate increase. Values of the position coordinate are positive or negative numbers multiplied by an appropriate unit of length, usually the SI unit of length, the metre (m).

2. The movement of a particle along a line can be described graphically by plotting values of the particle’s position x, against the corresponding times t, to produce a position-time graph. Alternatively, by choosing an appropriate reference position xrefand defining the displacement from that point by sx = x − x ref, the motion may be described by means of a displacement-time graph.

3. Uniform motion along a line is characterised by a straight-line position-time graph that may be described by the equation

where vx and x0 are constants. Physically, vx represents the particle’s velocity, the rate of change of its position with respect to time, and is determined by the gradient of the position-time graph

x0 represents the particle’s initial position, its position at t = 0, and is determined by the intercept of the position-time graph, the value of x at which the plotted line crosses the x-axis, provided that axis has been drawn through t = 0.

4. Non-uniform motion along a line is characterised by a position-time graph that is not a straight line. In such circumstances the rate of change of position with respect to time may vary from moment to moment and defines the instantaneous velocity. Its value at any particular time is determined by the gradient of the tangent to the position-time graph at that time.

5. More generally, if the position of a particle varies with time in the way described by a function x(t), then the way in which the (instantaneous) velocity varies with time will be described by the associated derived function or derivative

6. The instantaneous acceleration is the rate of change of the instantaneous velocity with respect to time. Its value at any time is determined by the gradient of the tangent to the velocity-time graph at that time. More generally, the way in which the (instantaneous) acceleration varies with time will be described by the derivative of the function that describes the instantaneous velocity, or, equivalently, the second derivative of the function that describes the position:

7. Results and rules relating to differentiation and the determination of derivatives are contained in Table 6. The derivative of a constant is zero, the derivative of f(y) = Ayn is df/dy = nAyn −1.

8. The signed area under a velocity-time graph, between specified values of time, represents the change in position of the particle during that interval.

9. Uniformly accelerated motion is a special case of non-uniform motion characterised by a constant value of the acceleration, ax = constant. In such circumstances the velocity is a linear function of time (vx(t) = ux + axt), and the position is a quadratic function of time ().

10. The most widely used equations describing uniformly accelerated motion are

11. Position x, displacement sx, velocity v x , and acceleration, ax, are all signed quantities that may be positive or negative, depending on the associated direction. The magnitude of each of these quantities is a positive quantity that is devoid of directional information. The magnitude of the displacement of one point from another, s = |sx|, represents the distance between those two points, while the magnitude of a particle’s velocity, v = |vx|, represents the speed of the particle. The magnitude of the acceleration due to gravity is represented by the symbol g, and has the approximate value 9.81 m s−2 across much of the Earth’s surface.

Kinematics – Motion in a straight line -motion equations

 

1. The most widely used equations describing uniformly accelerated motion in a straight line along a horizontal surface, which is taken as along the x-axis are:

Note: Position x, displacement sx, velocity v x , and acceleration, ax, are all signed quantities that may be positive or negative, depending on the associated direction.

For example, an object travelling at 10 m/s East, its initial velocity,  u   = +10 m/s as its direction, East is taken as the positive direction. After 2 seconds, this object then traveled at 30 m/s West, its final velocity will be taken as, v x = – 30 m/s, as its direction, West is taken as the negative direction.

2.  Another most widely used equations describing uniformly accelerated motion in a straight line of an object thrown upwards or dropped downwards perpendicular to the surface, which is taken as along the y-axis are:

 

Note: Position y, displacement y, velocity v y , and acceleration, ay, are all signed quantities that may be positive or negative, depending on the associated direction.

For example, an object travelling 10 m/s downwards, its initial velocity,  u   = -10 m/s as its direction, downward direction is taken as the negative direction. After 2 seconds, this object then traveled at 30 m/s downwards, its final velocity will be taken as, v x = -30 m/s, as its direction, downwards is taken as the negative direction.

The magnitude of the acceleration due to gravity is represented by the symbol g, and if it has a value 9.8 m s−2 (in the formula sheet near the Earth surface). Since the downward direction is negative, then the acceleration due to gravity = – 9.8 m s−2   

Accelerators and liquids in cans

 

Accelerators and liquids in cans

 

4×4 competitions

 

 

Problem to solve: How to transport liquids in the container (can ) without spilling?

In small groups:

(1) discuss the different  ways you can secure the  can in your effort  to minimise the loss of liquid in the can (the load )

(2) design simple experiments you can do to  observe the movement of liquids in the clear plastic bottle at different speeds or angles

(3) do the experiments and write up your observations in your blog.