Question

1. circle the chemicals that have the same groups of atoms: sugar, baking soda, corn starch, plaster of paris. 7) circle the chemicals that have different groups of atoms: sugar, baking soda, corn starch, plaster of pari. 8) which ones do you think are pure substances and which ones do you think are mixtures? why? (3)

Explanation:

Question 6: Circle the chemicals that have the same groups of atoms: sugar, baking soda, corn starch, plaster of paris.

Sugar (e.g., glucose, $\ce{C6H12O6}$) and corn starch (a polysaccharide, repeating units of $\ce{C6H10O5}$) both have carbon, hydrogen, and oxygen atoms in their molecular structures (carbohydrate - like groups). Baking soda is $\ce{NaHCO3}$ (has $\ce{Na+}$, $\ce{HCO3-}$) and plaster of paris is $\ce{CaSO4·0.5H2O}$ (has $\ce{Ca^2+}$, $\ce{SO4^2-}$, $\ce{H2O}$ - related groups), which are different from sugar and starch's atom groups. So sugar and corn starch have similar atom groups (C, H, O - based carbohydrate - like structures).

Baking soda ($\ce{NaHCO3}$: contains $\ce{Na+}$, $\ce{HCO3-}$) and plaster of paris ($\ce{CaSO4·0.5H2O}$: contains $\ce{Ca^2+}$, $\ce{SO4^2-}$, $\ce{H2O}$ - related groups) have different ion - based or non - carbohydrate atom groups compared to sugar (carbohydrate, C, H, O) and corn starch (carbohydrate, C, H, O). Also, baking soda and plaster of paris differ from each other in their atom groups (one has $\ce{HCO3-}$, the other $\ce{SO4^2-}$ etc.). But if we consider different from sugar/starch, baking soda and plaster of paris have different atom groups. Alternatively, any pair from baking soda, plaster of paris (since they differ from sugar/starch and each other). For example, baking soda and plaster of paris have different atom groups (baking soda: $\ce{Na}$, $\ce{H}$, $\ce{C}$, $\ce{O}$ in $\ce{HCO3-}$; plaster of paris: $\ce{Ca}$, $\ce{S}$, $\ce{O}$, $\ce{H}$ in hydrate).

• Pure Substances: Sugar (e.g., sucrose, fixed chemical formula $\ce{C12H22O11}$), baking soda ($\ce{NaHCO3}$), plaster of paris ($\ce{CaSO4·0.5H2O}$) are pure substances. A pure substance has a definite chemical composition and distinct properties. They are made of only one type of particle (molecule for sugar, formula unit for baking soda and plaster of paris).
• Mixtures: Corn starch is often a mixture (commercially, it may have impurities or be a blend of different starch molecules, but strictly, a pure starch sample could be a pure substance. However, in typical contexts, if we consider that corn starch as sold may have other components, or if we take it as a polysaccharide with a range of polymer lengths, but more accurately, sugar (pure sucrose), baking soda, plaster of paris are pure. Corn starch: if it's a pure polysaccharide (starch), it's a pure substance, but if it's a mixture of different starches or has additives, it's a mixture. But generally, sugar (sucrose), baking soda, plaster of paris are pure substances (fixed composition) and corn starch: if it's a pure starch, it's a pure substance; if it's a mixture (e.g., with other starches or impurities), it's a mixture. The key is: pure substances have uniform and definite composition (e.g., sugar has $\ce{C12H22O11}$ always, baking soda $\ce{NaHCO3}$), mixtures have variable composition (e.g., a mixture of sugar and salt has both, but here corn starch - if it's a commercial product, maybe a mixture, but chemically pure starch is a pure substance).

Answer:

Circle sugar and corn starch.

Question 7: Circle the chemicals that have different groups of atoms: sugar, baking soda, corn starch, plaster of paris.