Question 1 of 10
A student is investigating how the temperature of water affects how fast sugar dissolves. To make this a properly controlled experiment, what should the student do?
AUse a different amount of sugar at each temperature so you can see which temperature dissolves the most sugar the fastest
BVary both the water temperature and the stirring speed together in each trial so you can gather more data at once
CRun each trial only a single time to save time, then average whatever results you happen to get at the very end
DUse the same mass of sugar and the same volume of water in each trial, varying only the water temperature
Explanation
📌 In a controlled experiment, the independent variable (water temperature) is the ONLY thing that changes between trials. All other conditions — sugar mass, water volume, stirring, container — must stay constant. Otherwise, you can't attribute the observed effect to temperature.
Question 2 of 10
The Bohr model shown below represents a neutral atom. Based on the electron arrangement, which element does this model represent?
ASodium
BOxygen
CNeon
DCarbon
Explanation
📌 Total electrons in the diagram: 2 + 8 = 10. For a neutral atom, electrons = protons, so atomic number = 10 → neon (Ne). Neon's electron configuration 1s²2s²2p⁶ has the same 2-then-8 shell filling shown. Sodium has 11 electrons (one more in the third shell).
Question 3 of 10
On the periodic table shown below, which highlighted region contains the TRANSITION METALS?
ARegion I
BRegion IV
CRegion II
DRegion III
Explanation
📌 Transition metals occupy the d-block — the wide central rectangle of the periodic table covering Groups 3 to 12, periods 4 to 7. Includes iron, copper, zinc, gold, silver, etc. They typically form multiple oxidation states (e.g., Fe²⁺ and Fe³⁺) and have colored compounds. Group 1 = alkali metals (Region I); Group 2 = alkaline earths (Region II); Groups 17/18 = halogens/noble gases (Region IV).
Question 4 of 10
The element highlighted on the periodic table excerpt below is best classified as a:
AAlkali metal
BHalogen
CNoble gas
DMetalloid
Explanation
📌 Silicon (Si, atomic number 14) sits on the diagonal 'staircase' that separates metals from nonmetals on the periodic table — making it a metalloid. Metalloids (B, Si, Ge, As, Sb, Te) show mixed metal/nonmetal properties: they conduct electricity weakly (semiconductors). This is why silicon is the foundation of computer chips.
Question 5 of 10
The Lewis structure shown below represents which molecule?
AWater
BMethane
CCarbon dioxide
DOzone
Explanation
📌 Two double bonds between a central C and two O atoms = CO₂. The total valence electrons (4 + 6 + 6 = 16) are arranged as: 2 double bonds (4 pairs shared = 8 e⁻) + 4 lone pairs on the oxygens (8 e⁻) = 16. Linear geometry, no lone pairs on C, double bonds on each side.
Question 6 of 10
Based on VSEPR theory, which of the following best describes the shape of the methane molecule (CH₄) shown below?
ALinear
BTrigonal planar
CBent
DTetrahedral
Explanation
📌 In methane, the central carbon has 4 bonding pairs and 0 lone pairs. VSEPR predicts the four bonding pairs spread as far apart as possible → tetrahedral geometry with bond angles of 109.5°. Linear (2 groups), bent (2 bonds + lone pairs, like H₂O), and trigonal planar (3 groups, no lone pairs) describe other geometries.
Question 7 of 10
While transferring concentrated hydrochloric acid in the lab, a student should ALWAYS:
AWear only a long-sleeved shirt, since covering the skin with fabric is protection enough from splashes
BUse bare hands to feel the outside of the bottle so you can check whether it feels warm before pouring
CWear safety goggles, an apron, and gloves, and work near the eyewash station
DWork completely alone in the lab so that no one else can possibly be exposed to any of the acid fumes
Explanation
📌 Concentrated strong acids can cause severe chemical burns and eye damage in seconds. Standard lab safety requires goggles, apron (or lab coat), gloves, and proximity to safety equipment (eyewash, shower). Never handle reagents without PPE, and never work alone with hazardous chemicals.
Question 8 of 10
A student uses the piece of laboratory glassware shown below to measure exactly 50.00 mL of a solution. Which piece of glassware is shown?
AErlenmeyer flask
BVolumetric pipet
CBeaker
DGraduated cylinder
Explanation
📌 A volumetric pipet has a single graduation mark and is calibrated to deliver one exact volume (here, 50.00 mL) with very high precision (typically ±0.05 mL). The narrow neck and bulb shape are characteristic. Graduated cylinders have many marks (less precise); beakers and flasks are not for precision measurement.
Question 9 of 10
Which piece of laboratory glassware is BEST for measuring 25.0 mL of a solution with the highest precision?
AA 50 mL graduated cylinder
BA 100 mL beaker
CA 25 mL volumetric pipet
DA 250 mL Erlenmeyer flask
Explanation
📌 Precision hierarchy for volume measurement (most → least precise): volumetric pipet/flask > buret > graduated cylinder > beaker > Erlenmeyer flask. A volumetric pipet is calibrated to deliver one specific volume (±0.02 mL) and is the gold standard for transferring exact amounts. Beakers and flasks are for approximate volumes only.
Question 10 of 10
Magnesium reacts with oxygen to form magnesium oxide (MgO). Based on the electron transfer in this reaction, MgO is best classified as which type of compound?
APolar covalent
BIonic
CMetallic
DCovalent
Explanation
📌 Magnesium (a metal, group 2) transfers its two valence electrons to oxygen (a nonmetal, group 16), producing Mg²⁺ and O²⁻ ions. The opposite charges attract → ionic bond. Rule of thumb: metal + nonmetal with large electronegativity difference → ionic. Two nonmetals → covalent.