The purpose of this study was to compare the effectiveness of experimental and demonstration inquiry-based teaching method over lecture method to enhance grade eight students’ conceptual understanding and identify students’ alternative conceptions in acid-base concepts. The study took place in Eweket Fana primary school in Bahir Dar town, Ethiopia. The design employed was both quasi-experimental quantitative and qualitative designs (observations) approach. The sampling technique for the schools was purposive sampling and the classes were stratified random sampling from eighth Grade of Eweket Fana primary school. A total of 109 grade eight students randomly sampled out of two classes from five classes in Eweket Fana primary school in Ethiopia. The teaching-learning process accompanied for two months, which is three days per week, and 40 minutes for each contact. 55 sample students were involved in the experimental group and 54 sample students were involved in the control group. Students’ understanding and alternative conceptions of acid-base concept were evaluated with a pre/post-test design. The data obtained were analyzed using descriptive statistics means, standard deviations and inferential statistics paired-sampled and Independent-sampled T-test for quantitative data and thematic analyses for the qualitative data. The results revealed that there was a statistically significant mean differences between the experimental (mean =17.05, p = 0.000) and control groups (mean = 6, p = 0.000) on the conceptual understanding of the acid-base concept. After the intervention students in the experimental group showed better progress in eliminating their alternative conceptions as compared to the control groups. The experimental and demonstration inquiry method was an effective way for taught the acid-base concept. It is recommended to develop additional similar video demonstrations and video simulation to support the learning of neutralization reaction concepts taught in primary school chemistry lessons.