Directions: Use the information provided and your knowledge of Physical Science to answer the following questions. Show all work where necessary.
Directions: Use the information provided and your knowledge of Physical Science to answer the following questions. Show all work where necessary.
Source:
https://saraichinwag.com/what-happens-when-you-mix-lemon-juice-and-milk
Students add a spoonful of lemon juice to warm milk. Within moments, the milk begins to curdle, forming soft clumps called curds while leaving a watery liquid called whey. The texture, smell, and appearance all change.
Students ask:
Did we just make a mixture, or did we form a new substance?
This investigation helps them collect evidence that mixing can sometimes create new substances with different properties.
Some mixtures simply blend ingredients together without changing them, like sand mixed with salt. But other mixtures cause substances to change into new materials. When warm milk is mixed with lemon juice, the acid in the lemon juice interacts with the proteins in the milk. These proteins change shape and form new solid clumps called curds. This process is called coagulation.
Before the lemon juice is added, the milk is a smooth, white liquid. It has a mild smell and pours easily. After lemon juice is mixed in, the milk separates into lumpy curds and a watery liquid. The smell becomes slightly sour, and the texture becomes thick and chunky. These new properties show that the original milk is no longer present in the same form.
Because the substances after mixing have different properties than the substances before, this is a sign that new substances have formed. Students can observe these changes and collect evidence that this is more than just a mixture - it is a chemical change.
Property Observed | Before Mixing | After Mixing |
|---|---|---|
Appearance | Smooth white liquid | Curds + watery whey |
Smell | Mild | Slightly sour |
Texture | Thin, pourable | Thick, lumpy |
New Solid Formed? | No | Yes |
Time (minutes) | Mass of Curds (g) |
|---|---|
0 | 0 |
2 | 12 |
4 | 18 |
6 | 22 |
Look at Table 1. What changes do you observe in appearance, smell, and texture after the lemon juice is mixed with the milk?
Using Figure 1, describe what happens to the formation of a solid before mixing compared to after mixing.
Which observation best supports the idea that new substances formed?
How does mixing warm milk and lemon juice provide evidence that new substances can form when materials are mixed?
Respond using Claim, Evidence, and Reasoning.
Look at Table 2 and Figure 2. How does the mass of curds change over time, and what does this show about what is happening in the mixture?
Which piece of evidence is most important for distinguishing this investigation from a simple mixture?