why does baking soda and vinegar get cold
Bicarbonate of soda (or baking soda) is a chemical called sodium bicarbonate. Vinegar contains
acetic acid. we tested these two chemicals with red cabbage indicator, and found that a solution of bicarbonate of soda was alkaline, but vinegar was acidic. This week we made another solution of sodium bicarbonate with some indicator - it was blue just like before. But when we added a few drops of vinegar, the solution turned purple - neutral! The vinegar had reacted with the sodium bicarbonate and neutralised it. We did an experiment to find out more about what happens when the acetic acid in vinegar reacts with sodium bicarbonate. We all wore safety glasses to make sure nothing could splash in our eyes. What happened? The sodium bicarbonate and vinegar fizzed and we saw lots of bubbles. We could see that a reaction was happening. Then the balloon blew up! The bottle felt really cold around the mixture. After a while the mixture stopped fizzing and the balloon stopped expanding. The second group used double the amount of sodium bicarbonate and double the amount of vinegar, and their balloon blew up more. Why? When sodium bicarbonate and vinegar mix, they react with each other and one of the things that is made is carbon dioxide gas. The reaction needs heat to make it happen, so it takes heat from its surroundings, leaving the bottle feeling cold. The gas couldn't escape because it was trapped by the balloon. As more and more gas was made, the balloon blew up. Carbon dioxide gas kept on being produced until there was no vinegar or bicarbonate of soda left to react.
As we had captured the carbon dioxide inside the balloon, we could see how much space it took up. The gas took up much more space than the vinegar and sodium bicarbonate did! The group who used twice as much sodium bicarbonate and vinegar made twice as much gas, so their balloon blew up to twice the volume. What is carbon dioxide? Carbon dioxide is a gas that is found in the air. You cannot see it or smell it. When you add an acid to a carbonate, carbon dioxide is produced. Carbon dioxide is not poisonous - it is the gas that is used to make the 'fizz' in lemonade and cola. People breathe carbon dioxide out. All the people on earth are breathing it out all the time. BUT only a tiny fraction or 0. 04% - of the air around you is carbon dioxide! This is mainly because plants and algae use it up in photosynthesis. The picture on the right shows that most of the air is made up of two other gases - nitrogen and oxygen. At the end of this week's Science Club we made a volcano erupt! Our volcano was built out of playdough around a small bottle. In the bottle was a little warm water, a teaspoon of sodium bicarbonate, a few drops of food colouring, and a few drops of washing up liquid. When we poured vinegar into the top, the volcano erupted and lots of lava came out! It was great fun but rather messy! You can make your own volcano at home exactly as described above. You will need a small bottle, one with a fairly narrow neck works best.
If you do this inside, make sure you build your volcano on a large tray, or in a sink, or over several sheets of newspaper! The food colouring, water and dishwashing liquid are optional, they just make the volcano look a bit more impressive. You can experiment with the quantities of volcano ingredients to see what makes the best eruption. You could use a cardboard cone or some sand to build a volcano shape around your bottle, but why not make your own playdough? This is a brilliant easy playdough recipe (especially if you have little brothers or sisters - it will keep them entertained for ages). Mix together the salt, flour and cream of tartar in a large bowl, stir in the cooking oil. Get an adult to add 230ml of boiling water and give the mixture a good stir. It will be very hot! Once it has cooled down a bit, knead the dough well until it has a nice consistency. Add some food colouring and knead it in carefully - this can make beautiful patterns, but be warned food colouring can stain fingers! If you store the playdough in a sealed bag in the fridge it should keep for ages. Aside from bubbling, what else happens during a reaction between baking soda and vinegar? In each of the previous activities, students observed bubbling and learned that this was evidence that a chemical change occurred. In this activity, students will observe another aspect of the reaction between baking soda and vinegar.
Along with bubbling, students will see that the temperature decreases. A change in temperature is another clue that a chemical reaction has occurred. A reaction that results in a decrease in temperature is called an endothermic reaction. Be sure you and the students wear properly fitting goggles. The bulb of the thermometer needs to be completely submerged in the vinegar in order to get an accurate reading. Due to the small amount of vinegar suggested in the procedure, you may need to have students tilt their cups of vinegar so that the bulb of the thermometer is completely submerged. If your thermometers have a plastic backing, you may be able to lower the bulb by clipping the plastic backing so that it is even with the bottom of the bulb. Label 2 small cups vinegar and baking soda. Place about 1 tablespoon of vinegar and about 1 teaspoon of baking soda in their labeled cups. Note: If you plan to do immediately after this activity, increase the amounts to 4 tablespoons ( cup) vinegar and 1 tablespoon baking soda. These source cups can then be used for both activities. Download the, and distribute one per student when specified in the activity. An assessment rubric for evaluating student progress during this activity is via download on this page. For this formative assessment, check a box beside each aspect of the activity to indicate the level of student progress. Evaluate overall progress for the activity by circling either Good, Satisfactory, or Needs Improvement.
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