This activity on its own is a full lesson length.
Introduction:
Do you ever cook or help to cook at home? There is a lot of science in cooking - all that mixing and heating - lots of chemistry and chemical changes going on. We’ll make scones today and investigate the chemistry happening in our recipe. And then we get to eat our experiment!
Recipe for scones on the board:
1 cup flour
1 teaspoon baking powder
1/4 teaspoon baking soda
1/8 teaspoon salt
2 tablespoons melted butter
1/2 cup buttermilk
Mix into a ball, and divide into four pieces.
Bake at 400F for 15-20 mins until brown
Before starting, review or remind students how to measure accurately: take a scoop of the ingredient, then pass a finger over the top of the measure so that the ingredient fills the spoon but is not overflowing.
Students take turns to add the dry ingredients (baking powder, baking soda, salt) from the tubs on the table. The teacher circulates with a bag of flour and cup measure for this ingredient. Mix all dry ingredients together with the spoon.
Then the teacher circulates to add, or help add, the wet ingredients (melted butter and buttermilk).
Students mix all ingredients with the spoon, then use their hands to shape the batter into 4 scones.
Put on the baking tray, or on pieces of foil with the students' names.
Bake in the oven, keeping watch after 15 mins, and remove when the scones are browned on the top.
While the scones are baking, test for why the scones rise:
Tell students that in the oven some of these ingredients chemically react to make a gas. The gas bubbles push the scone up to make it rise, and make it light and fluffy.
To figure out which ingredients make a gas, mix different combinations of ingredients together in the wells of the paint tray. Mix any combination you like from flour, baking powder, baking soda, salt and buttermilk, using the coffee stir sticks to scoop the dry ingredients and mix ingredients together. Use a new scoop each time, so that the ingredients do not get contaminated with each other. (We will not use the melted butter as it is messy, and it does not make a gas.) If you only choose dry ingredients, add a little water, to allow proper mixing, and to mimic the wet environment of the biscuit batter.
Optional, but recommended: students to fill out the worksheet so they can remember which combinations made the gas. Younger students can draw what they find.
If students are mixing many ingredients together each time, prompt them to only mix two ingredients, so that they can figure out the minimal ingredients are needed to make gas.
Results should show these results with the fewest ingredients: the baking powder and water makes gas; the (warmed) buttermilk and baking soda make a gas (though slower in making bubbles and less obvious).
If time with older students: the chemical reaction happening can be shown with molecule modeals (see resource for purchase of molecule models).
H (loose hydrogen atom, present in sour things) + HCO3 (baking soda) ---> H2O (water) + CO2 (carbon dioxide gas)
Hand out their scones.
Before they eat it, ask students to break their scone open, and look for the empty spaces, where the bubbles of gas were. The gas made by the ingredients mixing made bubbles, which got stuck in the dough and pushed it up to make it rise in the oven. Then the scone baked around them.
